I am also working on a project that requires high-quality sound in and out. I’d really like to use the audio cape with the BBB, but not so much that I want to use special OS versions or patches. So I’m hoping that a mainstream (Debian?) driver solution will be coming that allows the audio cape – and HDMI video (HDMI audio is nice, but not needed much).
To get on with my work (software defined radio), I’ve been using a SoundBlaster 1240 USB card (~$80) that is very good. Possibly the cheaper SB1095 would be OK, too. Less expensive USB sound cards are lower quality – no surprise.