I am using the XDA-2 as a Preamp/DAC/Headphone amp. Since I only use digital inputs for my stereo set ups this works fine. It has two digital Toslink and two digital Coax plus an AES/EBU, which I use to connect my ERC-2 or ERC-3. Plus if you want you can use the XLR out to the amps while using the RCA outs for a pair of subs. I believe the DC-1 is set up the same way.
If you haven't bought the PT-100 yet, the DC-1 allows for an additional coax connection via its BNC input. It's a passive adapter that can be bought at Radioshack. I've also used the coax to optical converters to get more inputs. I heard there are Coax to AES converters as well but I think these may not be bit perfect. Though I wouldn't reccomend the XDA-2, it certainly has a lot more digital inputs as well.
Transport: Sony BDP 5100 Blu ray player spdif PC using Musiland Digital Times WASAPI via BNC connection - DAC: DC-1->XLR XPA-1 , RCA->Basx A-100 CD: Denon DCD 600 PCM 61 DAC. RCA Amp: XPA-1 gen 2 using XLR connections. Speakers: Axiom Audio m80 V3, Sennheisser HD700 headphones. two pairs 12 guage each bi-wire speaker cables per monoblock Headphone amp: Basx A-100 (INCREDIBLE VALUE!!)
Other equipment: Asus Xonar essence ST Behringer UCA 202 Sennheiser HD600