Re: How much difference do you think cables makes in the audio quality of your system
If you can avoid it I would not use wall connectors. I have attached a few pics with the plates that I use. I can't remember where I got them but they were only 5-6 bucks. They come in black and white, single or double gang.
In my room I ran bulk XLO Ultra II speaker cable to the fronts and center speaker. I soldered the higher end banana plugs on my self. It is a straight connection from amp to speaker. All three runs were over 40 feet back to the rack.
I would get the best cable the my budget allows and use it as one continous link. I normally wouldn't even bother with the bananas but I do a lot of demos so they are more convienent.
The standard cable we use for inwall speakers and most jobs is the Ultralink 12ga contractor grade. It's very high quality, twisted, and very easy to pull. From there I go straight to the XLO HT line and then up from there.
I used the same plate on the ceiling for my projector. I haven't put the black nylon hose over the video cables yet, so it looks a little messy.
Hope that helps.
As far as your question about adding "better wire" between your wall plate and speaker. I have never tried it, but my guess is the connection between the main run and the wall plate (most wall plates use crappy materials) would negate any improvement the "better wire" would have over one continuous run of the inwall wire. The key when running wire through walls and ceilings is cross electrical calbes at a 90 degree angle and if at all possible keep at least 24" away from power lines and light fixtures as you probably already know. Another tip is place your equipment rack as close to the speakers as possible, the shorter the speaker cable the better.