Arduino Volume Control

I have a line in (presumably coming from a computer or mp3 player) that I need to output to a set of car speakers.

I know I need an amplifier, my question is, what kind of amplifier can I get that will power 2 50W speakers and that I can control the volume of using Arduino?

Just need to be pointed in the right direction. Thanks!

Use any suitable amplifer rated for the 50W speakers and replace the volume control with a digital volume control.

Okay I'm getting the impression looking around that most amplifiers do have a built in volume control.

Random question. These are car speakers, running them indoors and not too loud, say typical tv volume. Any suggestions on what wattage amp i should get?

Depends on the size of the room and how loud you need it. 10 - 25 watts would be plenty for me, but your mileage may vary.

Speaker Ohms - "Most car stereo`s are 4 ohms" "Wattage is not loudness" "Decibels are Loudess"