Recently I added two Outlaw 755 amps to my set-up to drive 7 speakers and 2 subs. I calibrated everything with my SPL meter and it sounded great. I had some extra time, and the itch to tinker with something, the last few days and was curious if YPAO would add anything to the mix. I have used YPAO before I used external amplification and never found a discrepancy of more than .5 dB in any channel when double-checking with my SPL meter. However, with the external amps there were differences of up to 2.5dB on some channels. Another note and possible flaw with the 2500 if you choose the "Presence" option in the set-up and run all pre-outs to an amp, except the surround back channels. When you go to calibrate the channel levels the back surround pink noise bleeds through to the presence channels. The only way to prevent this is to actually choose "none" for the surround back channels in the set-up and then calibrate the presence channels. Until they give you the option of running all 9 channels at the same time, this is how I choose to leave my speakers. Still a great reciever or pre/pro and many people will never run into this unless they use all the channels and external amplification.
