DAC's in General

Most units have several inputs. I'm assuning you're looking for a DAC that has at least one of each input - optical, coax, and USB? The only ones I can think of that wouldn't allow what you're looking to do are the Ayre and Wavelength units, which only have a single USB input.

Yes. There are plenty of DACs with several inputs. Just check the specs to ensure that there are as many as you'll need -- and that they are the right types (optical, coax, USB) -- for what you'll be connecting.

Certainly. There are a lot of DACs with multiple digital inputs. The thing to watch is what the quality of each input is. A given DAC may have an acceptable S/PDIF coax input, but a poor Toslink or poor USB input for the computer. The thing that makes these different quality is the added jitter or the jitter from the master clock in the case of the computer interface. The clock jitter is THE MOST IMPORTANT thing in digital audio, even if we are talking about a CD transport. The best thing is to read the reviews, particularly online customer reviews if you can access these. I would not recommend trying to compare jitter specs. These can be very misleading and sometimes are outright lies.

Steve N.
Empirical Audio