I had the same recurrent problem with a SBLive 5.1 Xgamer card... I used to fix it by cycling the "micboost" button. Never tried your solution, It might have worked for me too... I got tired of fighting it, so when I bought my new MoBo I got one with onboard sound. Tried it, and have lost sound quality - but I don't lose my AHV anymore. A squaddie with the same card, had the exact same problem too.
SBLive card?