Oh boy, I'm so stupid.
I spent six hours this afternoon trying to understand why this old Sound Blaster card wasn't returning the correct value after a reset. I read all the available documentation on Sound Blasters I could find in google. I read the Linux and FreeBSD drivers to confirm that they do exactly the same as I was trying. Tried two different cards and they didn't work. And they would never work, unless you set up PnP correctly :P (Yeah, I checked all other details and forgot this stupid PnP thing. Oh well.)
At least I got some experience points, or so I hope.
Totally unrelated note: Edonkey2000 has a strange name, but it seems to work pretty well. The binary-only Linux client has a messy output, so I wrote a curses-based wrapper.