Hi OP. Stumbled across this site. I understand that you want to get the highest quality possible and also keep your gear from being outdated. However keep in mind the current and future avaliability of hi-rez content. In general 24/192 content isn't avaliable today unless you want to record it yourself. Hi-rez content is pushing 24/96 now and there's not much uptake as most people can't hear the difference between 16 and 24/44.1/48 much less 44.1/48/96. The future of hi-rez will probably hang around 24/96 for a while as anything higher 1. doesn't have large enough market to justify the R&D/manufacturing costs and 2. is just too much data to push through current consumer technology.
Upsampling your music to 192 may increase quality. But its upsampling and I'll avoid getting into the debate here. Also where to do it in your audio chain?
4 pin firewire is enough to get your data to the DAC. The 6 pin firewire carries power along with data. There are 4-6 and 6-4 pin adaptors avaliable. If you're shooting for highest quality, you'll want an independent, outboard power supply for your dac anyway. For convenience, a single 6 pin firewire will work...but your headphone amp needs power too so more cables.
There's no big difference between the studio route and the audiophile route...except in general, the Audiophile gear looks a little nicer and is more expensive. Sound wize, each piece of gear has its own sound, irregardless if its studio or audiophile.
I listen with DAC1, Mini-DAC, and Stello DA220, among others and have recorded with M-audio and RME stuff. For listening, I avoid running any of the DAC's via USB/firewire. Instead, a quality sound card (old Lynx AES 16) outputting AES/EBU is fed to the the DACs. Any upsampling or EQ is done with hardware instead of in the computer. Keep the computer a pure transport, get a good data stream out of it, and process everything down the audio chain.
True, hi-end, data-buffered and corrected, USB/firewire DACs don't exist yet. There's rumors of Wadia working on one for a while, but nothing yet. Lots of ADCs exist though.
If you really need a one-box solution try the mini-dac and dac1. I have a Mini-dac USB version that does work with Vista in 24/48 with some tweaking. Not sure if anyone's got the firewire version running yet. The Mini-dac has an excellent smooth sound that pairs well with the RS1. The DAC1 USB (24/96 on USB) is more detailed and dry, amplifying the Grado sound a bit much. If you REALLY like the Grado sound, try the DAC1. Avoid the M-audio and RME stuff as its more for recording and has too much features you won't be using (and additional electronics that'll interfere with playback).
Best solution is to find a PCMCIA vista compatiable sound card that outputs bit-perfect then connect that to a stand alone audio system.
Most studio gear will ouput both balanced and unbalanced. TRS-RCA IC's will work fine as you're just throwing out one half of the balanced signal. Pro gear may run at slightly higher voltages, but the nice thing about pro-gear is that its very flexible and usually has a way (internal jumper) to lower voltages to consumer gear.
And regarding the Edriol speeds, most recording gear will state the overall transmission speeds, not each individual channel. So, USB1.1 will support 2 channels of 24/48 which adds up to an overall 24/96. Most annoying.
