For what sources and what purpose? Setting every channel to full/large will defeat all the crossovers. Of course, that means that the sub out will only have LFE.
The subwoofer pre out's crossover in my ES receiver is fixed at 100hz and as far as I know is not defeatable. Unfortunately, the manual doesn't provide info on the slope characterisics. To avoid stacking filters, I use the LFE input on my sub with good results in my system.
However, a workaround you may want to try is connecting your sub with speaker-level connections from your receiver, connect you main L/R speakers from the sub, and then set your mains to "large" and subwoofer to "No" in your processor to feed all LFE through your sub's x-over.
Sounds like heresy not to use the line-level connection to your sub but the speaker-level route can actually sound very, very good. It will avoid stacking filters in the signal path which can lead to all sorts of distortions.