I've posted a webrev as well, and would really appreciate help with codereview.
Additionally, I've fixed the mixer a bit, to the point that I'm confident that a number of devices work perfectly. But some don't. Here's my test results so far:
- CT4670 -- (Sound Blaster Live!) verified 100% functional, including 4.0 surround.
- SB0100 -- (Sound Blaster Live! 5.1) SPDIF works, 4.0 surround works, no center/lfe output in 5.1 mode. Can't figure out why. (Would love to hear advice on this one.)
- SB0400 (Audigy 2 Value) -- works perfectly. Including full 5.1 surround, SPDIF output. I've not tested the side 7.1 channels because I don't have the necessary cable to do so.
- SB0350 (Audigy 2 ZS Platinum) -- surround sound on rear jacks works fine in 5.1 (can't test 7.1). My expansion box appears to be kaput though (doesn't work in Linux either), so I need help testing this from someone else who has a working one.