Well, if the horns play well enough to pass with 802s/adapters, I would not expect them to sound totally horrible with 288s.

When I speak out against the 511B, I am being a little bit picky... they are not "needles in ear" bad, just a little hard sounding. I have read forum posts claiming the E is a lot better (with 802s and adapters). 511E is not very common but I am sure somebody around here knows the horn.

If the 802 combo is tolerable, I suspect something more dramatic is at fault than corksniffing horn preferences.

Do you have a test CD or a way to hook up a laptop to the system to run frequency sweeps? Maybe you can hear if the driver is flipping out at certain frequencies...

One other possibility...are you sure the drivers are both wired in phase? Seems obvious but I recently picked up some 802-8Gs and one was wired backwards...that sounded very strange indeed. At first, I thought the diaphragms were fried.