Okay, this is gonna sound SUPER chumpy, but my Duo sound is working right now and that's all that matters. Ready to hear my super-duper fix? Are ya?
I left it on.
So I was getting kinda mad and depressed about the Duo sound problem, although I was a little heartened by the fact that I wasn't alone and that it's a common problem. So I was trying different CD and SCD games in it with no luck, then I put in YsI&II. No sound. I went to do something else, leaving the game running and just looping the intro. After maybe 10 minutes, I heard the CD music swell up. Fully expecting it to fade out again like always, I left it on. Amazingly, the sound didn't go away. In fact, I tried a few other games -- KO Beast, Snatcher Pilot Disk, CD Denjin -- and all of them worked fine, with full sound, from the word go.
I know it's a stupid quick & dirty fix, which can't even really be considered a solution to the problem, but maybe the darn thing just needed to warm up a little. I hadn't used it extensively in a while. Has anyone else tried this?