I've read reviews about CTK611 here (631 is just the same) and I expected more of this keyboard. It's brilliant to use as a MIDI keyboard with a function of non-computer sound processing. The best thing in it is automatic chord progressions. For $200 it's a good thing, but i won't recommend it to anyone who wants to use it without PC and something like SB Live!.
Comments About the Sounds:
Piano is good, drums are terrible. For $200 it's not bad perhaps.