A number of years back, I got an MU2000 module. It was original and not upgraded with the EX firmware. Its TG300B mode sounded very different compared to my actual TG300. It sounded much better to be honest. Superior samples and TOS link out, made it sound fantastic. Then I did the EX firmware update on it. This gave the unit the Roland GS sound map so you could use it instead of needing a Sound Canvas. Unfortunately it did this by replacing the TG300B mode. I didn't know that would happen (as the upgrade is not easy or well documented), and now I can't compare the two anymore. The GS mode on the MU2000 sounds different than a real sound canvas, because its still using Yamaha's samples. It still sounds great, just different. I still say its the best Yamaha sound module in their entire lineup. Just consider what you will lose if you upgrade to the EX firmware. The TG300B mode really did sound fantastic.
Interesting. I always assumed the "GS" update the EX firmware supplies was just a name change for the TG300B mode, as Yamaha finally had legal permission to use the GS name. MY 2000EX was from the later factory made batch, meaning I have never heard the non-EX version. If anyone wants to test this, the MU500 is probably the safest bet.
Modules: CM-64, CM-500, SC-55MkII, SC-88 Pro, SY22, TG100, MU2000EX, PLG100-SG, PLG150-DR, PLG150-AN, SG01k, NS5R, GZ-50M, SN-U110-07, SN-U110-10, Pocket Studio 5, DreamBlaster S2, X2, McFly, E-Wave, QWave, CrystalBlaster C2