Amp Broken, Need Help installing a new one!!!

[b13special]

Hey guys, I got a 2001 X5 3.0i, it probably has the most basic of features, there is an in-dash single CD player, no disc changer, none of the extras.
The speakers topped working one day, even though I could turn on the head unit and everything. I took it to a mechanic for some other problems about a week ago, and he fixed them, but he said that I need a new amplifier. He quoted me about $500 for a new stock amplifier, and I was wondering if I could put one in myself, and if I can , if anyone has any reccomendations on what amp to buy. If there is a guide somewhere that would be great as well.

I have a bit of experience as I installed my own amp and subwoofers in my old Jeep cherokee, so I was hoping I could do this myself.

Thanks for the help in advance!
Stan