There are different levels of XG and they don't always apply across the spectrum of synths and keyboards.

XG Level 1 (basic) has 32 note polyphony, 16 parts and reverb chorus and variation for the DSPs and 480 voices

XG Level 2 (MU100) has 64 note polyphony, 32 parts, reverb chorus and variation, and 2 insertion DSPs. The MU 100 has 1074 XG voices plus other modes with more voices

XG Level 3 (MU128) has 128 note polyphony, 64 parts, reverb chorus and variation, and 2 insertion DSPs.

There is now an XGLite which is a subset of level 1

When you look at PSRs, however, there is a mixture. The PSR740 and 2000, for instance, have 480 XG voices plus panel voices, 16 parts, reverb chorus and variation, plus 4 insertion DSPs, one of which is used for Vocal Harmony but can be used as a general insertion DSP via sysex. The PSR9000 has an extra DSP over the 740/2000 plus a few more panel voices. Yamaha claim that there are many effect types (e.g. the MU100 has 12 reverb types and 740 has 24 reverb types) but they're all presets and there are only 5 basic reverb effects. Same with the 2000 and 9000. So when it says that there are 102 effect types on the 740, there are really only 38 basic ones. The 102 are all presets. It pays to look in the back of the manual and decipher the gobbledegook just to see what you are really getting. It was quite an education constructing the XGworks updates for these keyboards.

Bryan