Turning my PC into an audio hub

Audigy2 has no problem outputting to a digital receiver. The only exception is DRM protected material. For example DVD-Audio discs cannot be transferred digitally over normal S/PDIF out/in (this is a universal problem/decision not related to Creative or Audigy). Also, if for example, you rip your CDs to WMA format and copy protect them so that they can only be played back on your own computer, Audigy will not output them digitally (i.e. it will shut off its digital outputs). I suggest ripping your CDs to a lossless format such as APE (Monkey Audio) or FLAC to preserve every bit of detail (and they will allow you to have a perfect copy of the original back on another CD if you need to). If you're doing lossy compression (e.g. because of space constraints) don't copy protect the files (Windows Media Player 7.0 and above protect the WMAs they create by default, disable it if you're going with WMA). I recommend either [--braindead] MPC compression or [LAME --preset extreme] MP3.

Consider this though: If you're using a digital connection, your sound card will not be the most important factor in sound quality. You can get the cheapest sound card you can find with a digital output and overall, it won't have too much difference in quality relative to a higher-end solution like Audigy2 or M-Audio Revolution. Speaking of which, if you'll be using analog output to the stereo amplifier/receiver (do stereo receivers have digital inputs at all? I know stereo amps don't, and a stereo receiver adds nothing but a tuner to the mix...) Audigy2 will be a good choice but the Revolution will be generally better in terms of sound quality.