Try without anything Matrox. You may still have problems with the audio, because of the 5.1 format @ 4.8 KHz. How did you ingest?
I have done with capture format
and master audio tracks in 5.1
and is red
AVCHD can not be captured. Capturing can only be done over firewire with tape based material (DV and HDV). Master audio track 5.1 requires the Surcode plug-in and is for output, not for ingest. If you have 4.2.1, you can ingest 5.1 audio, but it may require demuxing before ingest.
Recently someone sent me some AVCHD shots to test with. I tried putting them on the timeline in a correctly chosen sequence and I have to confirm that indeed the red bar is present. However, luckily even at full resolution there is no problem with playback, so it may indicate rendering is required, in fact it is not on my system. Even with numerous effects and transitions, scrubbing fast through the time line happens without hiccups, even with three or four video tracks in use and multi format material in the time line, like AVCHD 1080i 29.97, HDV 1080i 25 and XDCAM-EX 1080i 25.
So, while you are correct about the red line, it does not worry me, because I still have real time playback, despite keyframed 3-way CC, Gaussian blur, PIP, opacity, fast color corrector, echo, motion/scale/position effects, etc.
Your HDV capture mode confused me, but it was valid info, despite not being relevant here. Compliments on a well documented question.
For export, you don't need to render your time line. That is only necessary if you don't have fluid playback during preview. Lots of people never render their time line.
Hope this helps to remove your worry.