Mac,
I'm not trying to be difficult, but I don't think I truly understand your question: why are you asking for a DAC to match speakers? Your passive speakers are ran from the amp, so the speakers and amp need to be a good match - not the DAC-speakers.
Do your active speakers take analog or digital in?
Are you wanting to run preamp-less?
The need for USB input is clear. So either: a) DAC with asynch USB, or b) DAC with SPDIF in + a USB to SPDIF converter.
While b) is a bit counterintuitive, some people like Steve Nugent from Empirical Audio claim the clock is more critical for digital playback than the rest of the DAC topology, and that technology is evolving very fast. So maybe get a very, very good DAC even if it doesn't have asynch USB and add an Audiophileo 1 or 2 (about $150). In the not-too-distant-future the setup is likely to be outdated, but you would get a bigger bang for your buck by upgrading the converter only. On the other hand, you need to add the cost of additional cables.
Anyway, please don't take my questions as trying to be difficult. Trying to undertand your needs better so I can help you better.
cheers!
