Yamaha S30 is the 61-key version of the popular S80 synthesizer. I like S80's piano sounds better than XP30's. I also like the simplicity of Yamaha S80/S30's panel layouts - more intuitive than Roland XP30's. In terms of other accoustic sounds though I like Roland's JV/XP sounds much better especially the ones from their expansion boards. Both the XP30 and the S30 has two expansion slots. I personally like the Roland way of expansion, the Yamaha way requires more labor and care in handling the plug-ins. Roland has more choices of expansion boards but Yamaha has some unique ones like harmonizer, VL stuff. I own both the S80 and XP30 and I think they compliment each other well. If I am only allowed to choose one between the two, I prefer Roland XP30 for better allround sound choices and quality (just personal preference) and compatibility (GM) when used with computers. George Kaye mentioned that there is a GM set for S80 (should be applicable to S30) and Keyboard magazine's review on S80 mentioned that it is downloadable from Yamaha but I have not been able to locate that from Yamaha. With the GM set, S30/S80 should be GM friendly - I do not like their XG plug-in sounds. S30 can handle SmartMedia up to 32 MB, but XP30 can use only up to 4 MB.