[Bob Simon]

I have a stereo audio system that I put together around 20 years ago:
NAD 1700 preamp/tuner
NAD 2100 power amp
Magnaplaner MG-1 speakers

Audio Control Richter Scale crossover
Amber 70 power amp
Acoustic Research subwoofer (twin 10" drivers)

I've been completely happy with the sound and haven't kept up with
advances in audio technology or equipment. But at Xmas, I bought a
50" Panasonic plasma monitor so I've been thinking about adding a
Dolby decoder and need some advice.

A week ago one channel of my preamp/tuner went out intermittently. I
can get it working again for a while by momentarily blasting the
volume. Should I get it repaired or replace it with a modern
receiver?
If repair, can you recommend an external decoder?
If replace, what price range receiver will provide a level of quality
in line with the rest of the system?
Any specific recommendations?

I've heard that the center channel speaker should have similar sonic
characteristics as the main left and right speakers. What does that
mean? Sensitivity? What type of center speaker will work well with
the Magnaplaners? The available space is 15" x 47.75" x 21" (HWD).

I installed some inexpensive Boston Acoustics in-wall speakers in my
kitchen, which provide adequate sound for when I'm cooking. Would
something like these be suitable for the two rear speakers for home
theater? If so, can they be installed in the ceiling to fire down or
should they be mounted in the back wall (an outside wall).