Get another MMT-8. I have several of them, and it's the easiest, most flexible MIDI sequencer out there, not counting software IMHO.
There is a book called, "The complete Guide to the Alesis HR-16 and MMT-8 by Craig Anderton that explains EVERYTHING about them.
I know the memory on them is not so good, but there are sites out tere that show how to at least quadruple the memory. Defective displays can be repaired with a part from Jameco electronics.
Otherwise, look for the Kawai Q-80. It has 32 tracks so you can enter notes, etc.Then go back and use the second 16 channels to add controller and overdub effects. The drawbacks are finding floppy discs that will work with it.
Rig