I guess I should have specified that, sorry. I had the speakers hooked up (without the sub) in "large" mode. I'm still pretty surprised that an HK AVR520 can't drive the M80's in large mode with no other speakers connected. However, with the EP350 hooked up and the M80Ti's in "small" mode, everything seems to be OK.

Since "small" mode cuts the frequencies below 90hz off, is that where I should set the EP350 crossover?

And you're right, the EP350 is quite a capable sub.

Doug