Flat tickles your nuts and boost punches you in the gut. That's why on my 800, it's labelled the 'nad tickler/gut punch switch. Although on Slimpikins's 800 it's labelled ginfizz/disco fever 'cause that's how he swings.
Boost gives a really nice thump for music. If you make the bass hot, it will wallop you. Technically, what it does in my room is boost the band between 55Hz and 85Hz by 6dB. That's 4 times the power of flat within that band.
So why don't I just always leave it at boost? Because you have to rob Peter to pay Paul; that 4x power boost has to come from somewhere. Peter is the bowels of sub-bass and Paul is the mid-bass. So I notice when boost is on, effects wayyyy down low are still there but not as wind-flapping.
Let me tell you that if boost wasn't there, I would not complain with the 800v4. It really is the icing on the cake for me. Every time I boost, I give a little wink and a nod to Ian.
