Anyone got a Sony XM423SL Amp?

Thats the "Custom Fit" amp, could you tell me please whats involved in the
fitting? where does the amp get its power?
How does it turn on and off? Is it any good for a noticeable improvement?

Better still, has anyone got one fitted to a modern multiplex Citroen with
the standard fit CD players?

I've seen one new under £50 and think it could be worthwhile. I've already
got Sony 17cm custom fit speakers all round and aren't looking for mad bass,
but a nice sound.

I'm happy with the quality of the standard cd player, but some MP3 and
Radio2 could do with being a bit louder on occasions.

Thanks in advance
Ben