The difference in perception between MC decoding and an out-board audio processor is usually caused by dynamic range compression and dialog normalization. Both DRC and DialNorm is metadata information present in the bitstream on how to adjust the audio, but especially DRC can be considered harmful to the audio, as it reduces the dynamic range - which is especially true on a high-end audio system.
We do not believe that DRC and DialNorm are particularly useful, which is why we do not support them.
If you need DRC to enjoy a movie (because you are watching at night, on weak speakers, or in a noisy environment), we do have other DSP controls for that purpose.
Another option may be that the audio processor just has a generally louder volume level, which can alter our perception quite oddly.
Personally, I've not had any issues with dialog audio levels on a 7.2 system, and all speakers are calibrated to the same volume level using a volume meter and MCs room correction.