I would add an XG card to my box if I could ever find one . . . I actually thought I'd gotten my hands on one a few months back (The card had a chip with XG plastered on it in big letters.), but it seems like that card was actually some generic piece of junk based off of that cheap OPL-3, or whatever it is. No XG synth.
Yeah, you gotta be really aware of what you're getting when it comes to sound cards these days, 'cause it seems no one wants to include a physical hardware wavetable on their cards....which results in either "el cheapo" software MIDI only (read: craptastic M$-GS Softsynth), or a card that claims to have "XG MIDI support", but really is simply bundled with the "S-YXG100+" or the XG50, and then either has a physical MIDI FM synth chip for hardware, or no MIDI chip at all.....oy, I think I have a headache now...

I always thought that the SXG70 was both the XG20 and XG50, but I don't know alot about XG (or too terribly much about MIDI and synths in general), so I submit to you there, Goku.
You ARE correct, for the most part. The synth's "XGLite" mode corresponds to the XG20, while the "XGSoft" mode corresponds to the XG50. But, the slight difference here is that it may be using a beefed-up version of the XG50 engine that complies with the MU80 spec.
All I know is, the song I thought sounded the best out of them all using the SoftSynth & XG MIDIs is "Still More Fighting". I took the liberty of recording samples of the SoftSynth's Percussion Organ, and putting them in the SoundFont that I made, as well as a few other things to make "Still More Fighting" sound as close to the YAMAHA version as possible. (I cut and Pasted the Square Wave track from the XG version into the AWE version, to get the modulation effect . . . it doesn't seem like the newer SBLive! drivers use that method of modulation, though. It works with the older ones, however.)
IIRC, the type of modulation that's being used, isn't modulation after all, but is hard-coded into the preset's ADSR enveloupe (sp?). I suspect its part of either the "Sustain" or "Decay" sections of the preset.
And I TOTALLY agree about the XG "Still More Fighting" sounding the best, out of the various MIDI set versions.
The regular battle theme, however, while excellent in how it sounds with all the XG effects and stuff, is still lacking the awesome Squaresoft French Horn Sample (TM

) as part of its playback.
Finally, all of you who have both a copy of the S-YXG50/70/100+ and the FF8pc install cd, install the DM upgrade for the XG synth, as you can play around with it in Winamp2.7x/2.8x/2.9x, and it supports DLS level1.
I have been able to confirm that it will support simulataneous use of XG Variation Effects and custom DLS samples, but since installing the upgrade creates a new, separate DLS-compatible XG synth, you HAVE to use a DM-synth aware MIDI player like Winamp to access it.