Most of the USB DACs i've seen have been 2 outs i was just wondering how you'd add a sub to the configuration? would you need a 5.1 card aswell to run the out to the sub amp or can you get USB DACs with a sub out also?
this is in the wrong section, probably why you haven't gotten an replies.
basically the dac has 2 outs from there you can go to an active x-over (thats what i did) and then that'll 'steer' your audio signals to the right amp chans. (lows to your sub, highs to your door speakers). if you're fortunate enough to have an amp that has line level outputs and a decent internal crossover then you may be able to skip the active crossover and just go from the dac to the amp.
another option, if your amp(s) have internal x-overs is to get a rca y-cable to get 4 outputs from the dac and then set your x-over points on the amp.
New System in progress:
Phaze TD1500 ~> Dynaudio MD130
Phaze TD1500 ~> Seas g18rnx/p
Zapco Ref 500.1 ~ 12" tc-9
Behringer DCX2496 ~ Envision Electronics psu
Just to add to this. If you plan on splitting the outputs to multiple amps, make sure your DAC can handle the added loads. 2 or 3 should not be a problem for any DAC but I would check with the manufacturer to see if anything more then that would be a problem.