Choosing only one of the audio channels (left or right) and duplicating it (fill left or fill right) will help a little. You can also try eq’ing the audio tracks by reducing all the frequency bands except the vocal range.
When premiere is rendering a color correction (or any other effect) it is rendering it to whatever the project settings dictate. For example, if the project is a 48khz NTSC DV project that is what premiere pro will conform the renders too. Once it is ready to export it must re-encode the 48Khz NTSC DV format video into the MPEG2 format.
I use the MQ tapes for everything. My thinking is that I have a high end camera (compared to what I had in the past) so I will use high end tapes. In this case it’s the only end for tapes.