New Head Unit?

My Monsoon head unti spits the CD back out and says "Err" on it. Can I put an aftermarket head unit in? What will that do to the amp and speakers? I don't have the money right now to buy a whole new sound system. If I just wanted to by the Monsoon head unit, where could I get a good deal on one?

Does it only say error on sometimes?? I know when my car is cold or it just rained, I get an Err and it spits the cd out. If not, then yeah you can just replace the HU with a new one, just you might lose some functions depending on the type of Monsoon you have.