I have a THX Surround EX receiver and a center rear surround speaker set up. The only way to use EX is with the THX setting engaged. Now assume for a minute that I actually like the THX processing but notice the speaker levels are different than with just Dolby Digital, DTS, and DTS-ES. Should I set my speaker levels (with an SPL meter ofcourse) with the THX setting on and just leave it on with all the formats? Or are the different speaker levels actually an intended effect of the THX processing and I should calibrate with it off?