DAC as preamp w/subwoofer

Depends on the sub. Does it have line-level inputs and outputs?

Is this feasible with the W4S or with any other DAC for that matter?

It depends on several factors. Let us know the make and model of both the sub and the power amp, and how long the cable lengths will be between the DAC2 and each of those components.

Regards,
-- Al

Since you need separate outputs I assume you are not running your signal through the sub; even if your sub does not have a high level input, that is one driven from the amp speaker terminals, you can have a network built that lowers high level signal to line level. I use these with my Hsu subs and they work fine.