I was very specific the Waveforce's FM was an unintended side effect of Windows XP installing a generic Yamaha driver.
The XG could not equal the other, more capable cards, but it was cheaper, easier to find and did the job for most things.
I don't agree with you that the card was less capable. It certainly wasn't cheap eather. It went for about $130 at the time. For a gamer card it was fine (at least for me). Wavetable sounded better than the PCI Sound Blasters at the time. You may be right about it's OPL compatible core. I can say from experience that it had excellent DOS support for a PCI card.
I guess having actual experience with this sound card has given me a better (though biased) impression. So what other more capable cards do you know can do MIDI FM under XP?
@Ari: Yes it came with a bunch of classical midis. I forgot about those. I always wondered if those were tweaked to sound best on Yamaha hardware.