Bass is a very subjective thing and I also don't know what speakers you are running, so take this with a grain of salt. I just think that 80hz is too high of a crossover to set *all* your speakers.

If I set all my speakers at 80hz, based on my speaker mix and how I listen to my system, that would just send too much low frequency information to my two subwoofers for my taste.

Also, based on how the 990 "combines" the signals from various channels (in certain modes) to send to the subwoofer, I would notice drastically more bass in a mode like Stereo-7 than I would in other modes - even more so at 80hz. So all my speakers are crossed-over at 40hz (your mileage may vary).

Just my 2 cents' worth. I hope it helps.

[edit] I just noticed that gonk's post also mentioned turning down the cross-over setting as a possible solution. Sorry for being repetitive.