Catching more than 2-3 keys simultaneously

[nitro2k01]

I think I'm pretty much out of luck, but I'll give it a shot anyway. Is there any way to catch more than 2 or 3 keys simultaneously? Right now it just beeps when I mash too many keys.
This is important for me since I use a live breakbeat sequencer that could use that. What I remember usual PS/2 keyboards have a 4 or 5 key limit, depending on position?
My current solution is to use a USB keyboard that seems to be just about unlimited in this department. But the disadvantage of that is that not portable of course.