I have a UPA-2 (not the UPA-200) and it is almost the same as the XPA-200 with minor differences. I have also used an XDA-2 (and1 1) and USP-1 and XSP-1 and DC-1 in my system.
Here's what I noticed.
The XPA-2 is the superior amplifier. It is very fast. When coupled (and especially when coupled!) to a dedicated pre-amplifier like the USP-1 and XSP-1 you can hears some really incredible sound reproduction.
The XPA-2 is REALLY heavy. It doesn't look that big on the product page, but damn it is heavy and I love it! Talk about build quality. If you open up your XPA-200 you will see how good it looks, open up the XPA-2 and you'll see you are paying for twice the build quality and parts. Can't say enough about it! It also has more capacitance than it's listed as I think it has 80,000 or 120,0000mf....just wired in a different way to produce the 45,000 it's lsited with.
The main difference is that the amp goes from zero to hero in volume very fast. The XPA-200 has a smearing to it which is part of its sound signature. Don't get me wrong, I think the XPA-200 is a fantastic amp, but this is just faster at doing stuff. Lonnie mentioned that he purposely increased the slew rate for this amp.
Where the UPA-2 feels laid back and ever so slightly dark background (in a good way) , the XPA-2 does not have this sound signature. It feels slightly clearer. It also has more control in the bass.
The USP-1 had fantastic dynamics, unfortunately everything felt a little "agressive" in the mid-range. Sort of like the sound was c oncentrated around it and too "focused". The treble was a little "elecronic" in sound. But in terms of dynamics you can't fault it...wow!
The XSP-1 brings its improvement where it doesn't have that agressive mid-range. It is basically the USP-1 perfected. All its "faults" have been addressed and it has a difference in sophistication. Basically top to bottom balance is very well done. It has an "analog" sound to it. It doesn't feel artificial in the treble. It has a slightly laid back sound signature in the treble feeling ever so tiny bit not quite as impactful in the highest registers at lower volumes.
But.....having said that, this was minor and I didn't have a problem with it. Also at lower volumes it sounds really good which isn't something DAC direct to amp has shown me to be capable of. It has very good placement of instrments and its dynamics can knock you off your feet.
It's improvement over the USP-1 other than better top to bottom balance especially treble is that it feels like it is CLEARER and more resolving of more subtle details.
The USP-1 was right at home in a theater environment with fantastic dynamics and impact. The XSP-1 is right at home in the music enviornment with nuance and natural sound.
Now when I combined the DC-1 to the XSP-1 in another friend's room, the results were surpringly poor. The mid-range felt bloated and muddy and very slow. With very little treble and the vocals appeared to be coming fom far away. However that may be a one time thing with some unknown third factor as others have used the XSP-1 and found it to sound fantastic with the DC-1. But I'm throwing it out there as that was my experience with it.
The DC-1: is a very nice upgrade from the XDA-2. It's stregnth is in its mid-range. It can produce a more coherent sound over the soundstage. Rather than various instruments positioned everywhere, it can knit the various instruments against the ambient background of the soundstage so that they can "relate" to one another than make it sound like they were recorded separately. Instruments also have a bit of a 3 dimensional quality. For instance in Glee, where Rachel sings make you feel my love, I could literally hear her voice being produced in her throat, when she closed her lips I could hear the nasal passages produce a different part of the vocal and I could hear her breath very clearly as she sang. Something that did not happen in the other dacs. It was stunning when I first heard it
Its treble is a little laid back and the mid-range low bass may be a bit more pronounced than I would like.
Having said that, the best sound I have heard is an oppo 105 coupled to the XSP-1 which I felt did better than the DC-1 but it also is more than twice the price. The Asus Xonar essence ST with its Burr brown mutli bit 1792 DAC did better in slightly more subtle details than the DC-1 but it needed a dedicated pre-amp to bring its best out. It wasn't better than the Oppo 105
