The Stan track sounds a bit like a Yamaha MU device. Another synth used a lot in the era was the E-MU Proteus line, 1 and 2 at that time.
The piccolo (I don't think it's a pan pipe?) in the Circus theme sounds like the MT-32 a bit. The drums sound like a Roland sample set to me, possibly mastered to give a different sound. Could be the Roland U-220 as well, another Sound Canvas similar synth but with better quality samples and components.
The overall sound is very Roland to me still, the shakuhachi sounds I'd almost bet come from a Roland (possibly even a LA one). Check the SCUMM Bar for example, it sounds very Roland to me. Bass, drums, brass.. LeChuck's theme too. Voodoo Shop is interesting, sounds part Roland and part not like the drums you've touched on before. Possible that comes from something else. Or it's a drum kit I'm not familiar with. Then the Following the Shopkeeper track is clearly Roland drums.
So possible Roland synths from the era are:
- LA Synths (MT-32, D-110)
- SC-55
- U-220
- MV-30/D-70
- early JV synths maybe (eg JV-80)
- Samplers
To give an idea, the U-220 was heavily used on Mark Seibert's "Sierra Soundtrack Collection" CD from the same year as SOMI. As was the Roland S-750 sampler.