Advice needed on simple whole-house audio system

["Alex" <alex1138@xxxxxxxxxxx>]

I would like the expertise of some of the posters here on how I can
build and install my own (simple) whole-house audio system. My
requirements are fairly easy...I only need one zone, and the indoor
audio will consist of one (mono) speaker in each of three rooms. The
outdoor audio will be three pair of outdoor speakers in my backyard.
The audio source would be whatever is coming out of the line-out ports
of my family-room A/V amp, which would be the MP3 I'm listening to, or
the movie I'm watching. The interior sound quality just has to be 'good
enough', that is, some background noise for dining or party guests.

I have posted a diagram of what I THINK I should do at:
http://home.comcast.net/~alex1138/whole_house_plan.jpg

I had planned on installing a panel in the wall behind my family-room
stereo, to take the line-out of that amp up to my home office closet
and into a stereo amplifier. From there, the amplified signal would go
up into the attic to a distribution panel. There, the amplified signal
would be split into the various cables to go through my attic, down
into the walls of 3 rooms to volume controls, and then back up into the
attic to mono, ceiling-mounted speakers. Same thing for the outdoor
audio, but into pairs of stereo, outdoor speakers.

I have a few questions...first, is this plan okay, or am I
underestimating what needs to be installed? It seems less complicated
than I expected, even for what I think is a simple system.

Also, I will use high-quality cable to carry the amplified signal
everywhere it needs to go, but do I need to also use high-quality cable
to carry the unamplified signal from the family-room source to the
amplifier in the office closet?

Finally, I had read that I should use 'impedance mathching volume
controls', but I must admit I'm not sure what those do for me. Do they
ensure that turning up the volume in one room won't diminish the volume
in all the other rooms?

Any help that can be offered would be greatly appreciated!
--Alex