What I'm seeking is flexibility, hopefully at no penalty of diminished sound.
A very common scenario with pre-pro's is failure to keep up with new formats in a timely fashion at reasonable cost. Compare this with the HTPC world, where DVD software, video card, drivers, sound card, powerstrip etc. are all constantly evolving and improving. I would love the former to be more like the latter, and moving pre-pro functions to a sound card with the potential for software updates as well as hardware improvements that are relatively inexpensive may be the way to accomplish this. I currently own a Proceed AVP with no inputs for DVD audio, no DPL 2, none of the newer DD or DTS formats. I passed on an expensive, bug-ridden upgrade offered a few months back. I would love my next processor to be more like my DVD player -- major improvement a month or so ago for $70, instead of shelling out megabucks every few years.
Granted, some pre-pro manufacturers do better than others with updates. However, you are investing in a proprietary format, and are limited to whatever that company may offer, limited by commercial viability, financial health etc. The PC is an open format. You could go with an Audigy II and PowerDVD now, switch to Theatertek 2.0 and a M Audio Revolution later and so forth. Whatever looks best can be rapidly incorporated.