I don't think I've ever dealt with a more frustrating card... 😵
Once upon a time, I'd hoped to pair a SW20-PC with an SW60XG in a two-slot system, which would have made for some sweet, sweet Yamaha aural goodness. And why shouldn't it? Yamaha designed them both, after all. Imagine my disappointment then, upon discovering that the SW20-PC is ridiculously noisy, all thanks to its wonderful Karaoke Processor chip (that, due to an equally ridiculous design, cannot be bypassed. Whoops!).
And so, what ought to have been a reference OPL4 design simply isn't.
Incredibly, it gets worse...
You see, recently, I figured I'd give the SW20-PC another go, and discovered something rather neat in the process: The YMZ290 chip spits out FEh (ACK) bytes. Therefore, not unlike the Ensoniq Soundscape cards, games requiring an "intelligent-mode" MPU-401 interface will also work with the SW20-PC. This is all fine and well, assuming you want to play-back MT-32 scores via the OPL4 General MIDI soundset, but who wants to do that, right? Not a problem - just hook up the ol' MT-32, via the joystick port, and...
Apparently, the SW20-PC does not support external MIDI in DOS. Good one, Yama-ha-ha-ha!