the XG chip is not bad at all despite being 25+ years old
Yes, the chip is a full implementation of Yamaha's mid-nineties version of MIDI XG.
It can handle sound layering, splits, and velocity layering. In addition to the amp envelope and filter, each voice has a pitch envelope under the hood, and the LFO can be set to modulate filter, amp, or pitch.
If you dig deeper, each note of a custom drum kit has individual filter, amp, and send parameters, including a second delay parameter you can only access with Sysex.
Sound On Sound has a great three-part series on using XG tone generators for sound design:
With all of this functionality, you can create additive synthesizer patches, various subtractive permutations including transwave emulations, and a bunch more. There's even a way to make it into a step sequencer with per-step, realtime adjustable pitch/volume/pan/sends (described in the article). And if you get familiar with the voices, some of them let you control filter envelopes.
