Hey what up bluescreen.
The main differences between the e5000 and the e6400 ultra models is that the base e5000 model only has 4 outputs and can be upgraded to 12 while the e6400 has 8 I believe and can be upgraded to 16 (I'm an e5000 owner). Also the e6400 base install has 64 voice polyphany that can be upgraded to 128 while the e5000 has 64 voices and cannot be upgraded to 128. The e6400 has a blue back lit screen while the e5000 has a greenish yellow back lit screen. The amount of factory RAM is higher with an e6400 I think. My e5000 came with 4 megs of RAM but, of course, I maxed it out. Both units max out at 128 megs. Those are the main differences but if you are buying the equipment used you may have other upgrade options installed. Other than the differences I mentioned there really isn't too much difference. I've had my e5000 for quite some time and cost was what was the deciding factor when I purchased it. But these days both units are very cheap used so I would go with the e6400. Good luck.