Just wondering if this may be part of my problem (see post about auto shutoff). When you say initially set to -8db, are you talking about the level setting in the receivers menu, or adjusting the gain knob on the sub, so that the reciever reads it as -8? I'm not sure what you are adjusting when you refer to the sub trim level, is this the gain knob or the receivers level setting?
As D-bone pointed out I am referring to AVR sub trim. When I set my XV-15's amp gain at 1:30-2:00 and then run calibration, Ypao sets my Sub trim -8. I then bump my sub trim up to 0(or a better way to think of it is 8db hot), which sounds the best with HD Cable, Pandora, Internet Radio, or any compressed form of audio. Now If I pop in a Blu Ray the subs are way hot, so I pull the AVR sub trim back to -3. That being said once I run calibration I never touch the amp gain, only adjust the sub trim. Again I shoot for -8 on initial calibration so I have up to 8db of adjustment in the AVR sub trim without going past 0 or positive. Also if your AVR trim is below -5db it can mess with auto on.
The point to all this(hopefully I am doing a better job explaining this time) is, if you set the PSA sub amp gain around 12:00, the avr calibration will be at or around 0(atleast this is where it is on my setup), Which is what the standard procedure is. the problem with that is if your bass sounds weak with compressed audio sources(HD cable, Pandora., Internet Radio)then you have to boost the sub trim into the positive range which can and most likely will clip the signal before reaching reference level (0) on the master volume.
The way you have it now should work the best with multiple sources. If the bass is too hot on a blu ray back it down -3 in the AVR. You will have to play around and find the sweet spot.
Sorry not trying to sound like a broken record lol. Hopefully this makes more sense.