I have the same desire- a small 4CH amp to power my stock-size speakers for the empeg.
I haven't had any luck at the usual component-review sources on-line. It seems that physical dimensions are the last thing on everyone else's mind.
I'm tempted to get another head unit, just to stash it away (only have room in the dash for one DIN1) and leave it set to AUX...
The problem there is that I can't decipher whether the aftermarket units have an AUX IN that I can use. Seems that piece of info is not too interesting for the majority of folks- either that or it's a given that I'm just not aware of.
If it's possible to put a 50W/CH 4CH amp in a DIN1 unit *along with* all the rest of the radio/CD/whatever, then why, why, why are all the amps so freakin' huge?
10"x12"x2" is just gross!