Here is my impression:
my gears: Denon avr-3805, Axiom M60,VP100,M3.
default setting from Denon : FL/FR/Center/SR/SL=LARGE and Sub=yes with crossover=80hz
When I first play one of my CD, M60 gives lots of bass like i've never heard of bass before, clean and tight. And I play it with default setting from Denon.
THen, when the sub arrives and after running auto setup in Denon, the bass is much louder and better.
After a while, I turn off the sub ,the bass seems to be weaker. I think it's just because I get used to listening to music with the sub already.
However, it also depends on the source as well. In general, I turn off the sub when the source produces too much bass, otherwise, i leave it on or manually turn down the volume on the sub about 10 o'clock setting (11 o'clock when i watch movie). I read somewhere that you will have to adjust both gain control and volume control of sub to match the main speakers. By the way, auto setup always set my FL/FR to large and center to small.
