I just installed a similar setup in my Pathfinder last week. I have the 9853 and the iPod interface. I can't say enough good things about it. SQ is definitely 10x better than using an AUX input, because the HU does the MP3 decode, and applies MX settings in the digital domain.
I am in the process of re-encoding my CD collection using EAC and the LAME MP3 encoder, as the old tool I was using made the bass frequencies distort. I didn't notice this until after listening to a few albums I encoded vs. some MP3s from a friend's Ipod in the car.
My gripes are few, but include:
-Not being able to show artist/title. Of course, this isn't necessary because you usually know the music in your collection.
-Searching by artist or album is tedious at best with the GlideTouch. It's a great interface (IMHO), but I would have liked a "fast scroll" button or something to go along with it. Basically, if you run your finger across the bar quickly, it skips something like 20 artists or albums at a time. This is easy enough while you're sitting still, but will prolly cause an accident if you are driving. Of course, the PF's radio is a good arm's length away from the driver's seat position.