WTF? EQ won't eliminate phase cancellation. A digital delay is pretty much the only solution that will work if you have the equipment to be able to see the phase well enough to know how much to offset the left signal from the right.

Sound waves are like ocean waves - phase cancellation occurs when a wave that is cresting up meets it's opposite cresting down. EQ might keep a few specific frequencies from colliding (I wouldn't even bet on that actually) but it's not possible to EQ all of the summed frequencies enough to prevent all cancellation.

This isn't just a discussion going on here but in every keyboard discussion forum on the web currently. Many people have been trying all sorts of tricks to prevent phase cancellation, and so far the only viable solution I've seen is by delaying the left or right signal just enough to keep the phase problems from happening. I even read where one person was trying to use a short cable on one channel and a very long one on the other when running stereo keyboards to a mono amp... obviously this isn't an exacting way to solve the problem but I think it's on the right track.

The people who are using mono amplification are just learning how to live with the reduction in sound quality. The ultimate answer is to just try your rig in mono and stereo and decide for yourself.