Has anybody ever replaced these units with an aftermarket one? The one in my wifes 850 has given up the ghost.

 

Haven't done it myself (yet!) but there's plenty of posts talking about what others have done.

You can head over to crutchfield.com for fairly good prices on aftermarket head units and they'll sell you a wire harness so you don't have to cut wires, a bracket to fit in the factory space and a spacer if you go with a single DIN-sized unit.

 

Yes, I replaced mine in my 940, my 850 and my current volvo, which is an s60r. It was very easy but I would recommend getting a wiring harness.