Here's what Stereojeff posted at the AVS forum:

You are correct: distance and level are not user adjustable when Trinnov is engaged. The rationale: Trinnov measures distance to the millimeter including physical delay caused by actual distance and phase delay caused by crossover filters. We know of no way that the user would be able to improve the automatic measurement. As to level, in the home Trinnov's ability to re-map the soundfield is one of its most remarkable features. Remapping cannot work unless phase, frequency response, output level and distance are fixed.

However, it appears that the LFE level can be adjusted after Trinnov mapping:

LFE is independently adjustable. So is your subwoofer level--at the sub. Regarding the others, please keep an open mind until you hear the receiver with Trinnov engaged.

In my experience, having the ability to raise the center channel volume ("trim level") on my 950 is very important. Way too many movies have the effects and/or music just too loud in relation to the dialog, at least in plain old dolby digital. Is this problem better or worse on Dolby True HD/DTS HD lossless audio?