I'm just going to sprinkle in a few comments to go with some of the listed items (not at all exhaustive).
1.
Almost everything these days does or can run Windows 10 Pro (but NOT Chromebooks and obviously not Macs).
(The only big difference between Home and Pro is some options to defer updates - but that's worth having.)
If you plan to run Windows 10 then you are much better off getting a machine that comes with it already installed.
Windows 10 is a throw-in with most computers when you buy them...
However, adding it to a machine that didn't come with it will cost more, and you MAY run into hardware compatibility issues.
(The license is tied to the hardware. In theory, if you replace Windows 10 with something else, like Linux, reinstalling Windows 10 later should be trivial.)
I should also mention that, if you purchase a refurbished machine, even a relatively new one, there is no guarantee it will work with Windows 10.
This will be no problem if the machine originally came with Windows 10.
However, there have been lots of compatibility issues with computers that originally came with Windows 8.0 or Windows 8.1 NOT running Windows 10 properly.
(So, if you buy a refurb from a shop, even if they've installed Windows 10 on it, if it wasn't originally loaded with Windows 10, you may discover odd problems later.)
3.
Most modern processors generate a lot of heat... especially when working hard... so fanless cases tend to be the exception and to be somewhat expensive.
Also note that many small quiet machines have relatively little processing power.
And some small laptops that run very quietly and get really good battery life do so by throttling back on the processing power (Intel's new "portable CPUs" do this automatically).
There can be two problems with this...
First, when asked to deliver significant processing power, most of them speed up... at which point some go from dead quiet to rather noisy when the fan kicks in.
Second, if you have a low-powered processor that is constantly throttling up and down, it can cause odd things to happen when playing audio... like dropouts.
(At which point you end up disabling the power management... at which point it may not be as quiet as you'd hoped.)
Luckily many modern fans are relatively quiet.
(It's also somewhat difficult to entirely avoid fans... even my cable box has a fan... as does my Blu-Ray player.)
4.
Internal optical drives are becoming less common these days.
This will also limit you to a desktop machine since almost no modern laptops include them.
(If you plan to add one make sure you choose a machine with an externally-accessible drive bay.)
5.
Internal SSDs have become very cheap and this should be no problem as a purchase option (a 256 gB SSD should cost about $60).
It's also no problem to swap in an SSD after you purchase the machine, or swap in a bigger one, if need be.
NOTE, however, that different vendors feel quite differently about doing this.
Some will offer support if you need help doing it...
Others may consider it a "modification" and void your warranty...
6.
You will find very few manufacturers who offer a large spinning drive internally as standard equipment.
And, as an optional extra, they tend to charge way too much.
But it should be simple enough to add one yourself (make sure you have extra drive bays).
7.
Everything comes with HDMI these days.
8.
Being able to run headless is a feature of the operating system.
Windows tends to want you to log in.
IMPORTANT NOTE ABOUT WINDOWS 10 HERE.
Windows 10 asks you several questions about things like linking your computer to an online account when you first set it up.
Many of these settings are VERY difficult to go back and change later.
Do your homework BEFORE you start up your new machine and configure it.
Or be prepared to have to re-install Windows later if you want to make major changes.
One example is that, the first time you run the computer, Windows will prompt you to link it to an online Microsoft account.
This actually seems unavoidable.
However, it can be avoided, if you press Enter and Skip on the right screens.
BUT, going back and changing it once you've set it is VERY difficult, and may end up requiring you to reinstall Windows.
9.
EVERY desktop machine comes with a fast Ethernet card these days (it's often not even mentioned in the specs).
Many modern LAPTOPS DO NOT come with a wired Ethernet port - and many require you to use an annoying USB dongle (they expect you to use wireless).
10.
All "normal" USB ports are pretty much the same....
And most audio applications don't even require USB 3 (which is now standard).
There are some "fancy audiophile USB ports" but whether they make any difference at all is uncertain.
(Some provide isolation, or especially clean USB power, which SOME USB devices MIGHT benefit from... but I wouldn't bet on it.)
11.
Optical S/PDIF (Toslink) is still found on some desktop machines or laptops - including some Dells (but not many).
Coax S/PDIF is quite rare on normal computers unless you add a separate card.
12.
Bluetooth is pretty common.
There are also a wide variety of wireless keyboards and mice that run using a proprietary USB dongle.
(Logitech makes a bunch, including keyboards, mice, and tracballs.)
You should also keep in mind that, in general, the purpose of something like a NUC is to AVOID extra functionality.
They are specifically intended to be optimized to do a certain specific thing well - and NOT do other things.
(So, for example, they expect you to RIP your CDs on another computer, and then load the files onto them via network, or store them on a separate network drive.)
I also have a piece of advice about setting things up.
When you first get the machine, set up Windows, install the programs you plan to use, RIP a few dozen CDs, THEN USE IT FOR A WHILE.
DO NOT RIP thousands of CDs, or spend a lot of time loading stuff, until you've played with it for several weeks.
Then, once you're sure you're happy with how it works, go ahead and load everything onto it.
(That way, if you discover you're not happy with some of the choices you've made, you won't lose much by reinstalling everything and starting over.)
(And, while doing so, DOCUMENT EVERYTHING, so you'll know which settings to-reenter and which ones to change next time.)
Seems I'm in over my head (not an unusual circumstance), and would like a bit of information from the Loungers, please.
What I'd like to have (ideally), and so far as I know, is a living room music server that offered all of the following:
1. Ability to run Windows 10 Pro (should I choose to stick with jRiver server software)
OR to run the proprietary Roon-based Linux system (should I choose to use Roon)
2. A low-profile case (<6" tall) to fit in my equipment rack
3. Either fanless operation with LOTS of heat sinking or else a really, really quiet fan
4. Internal optical drive for ripping discs (NOT optional)
5. Internal 256 Gb SSD drive for the operating system
6. 3.5" internal 6Tb drive for data storage (NOT optional)
7. HDMI video output for use with the TV for when setup is needed
8. Ability to run "headless" if I don't want to have the TV on when listening to music
9. Ethernet connection for network access (but will not stream music via Ethernet)
10. High-quality, high-speed USB ports (will be the main music output method)
11. I'd also like a SP/DIF coaxial audio output if possible (but this isn't absolutely necessary, provided the USB is excellent)
12. Bluetooth or wireless ability for keyboard/trackpad and iPad controller
13. Reasonably fast processor & at least 8Gb RAM
Is there anything I've forgotten?
The goal, here, is to have a single box without appendages dangling on all sides. I'd prefer to avoid external USB HDDs, external optical disc readers, and adapters for various functions.
I see a wide variety of technologies available (NUC, ITX, Compact brand boxes with proprietary sizes, etc.) and am not sure which is appropriate for my needs. I might as well ask my desk as to ask the kids down at the local Best Buy or Office Depot, but I'm sure that you Lounge members would know these things. So thank you in advance for your expertise, Boomzilla.
[/quote]. Also this way you may find that you'd have to alter your original paramters to get within your realistic price range. 
