I have to agree with Topless. The factory radio setups are crap and if you're going to replace, replace with quality stuff. Audio equipment is much cheaper nowadays and as mentioned, you can get a good setup from Crutchfield in the $500 range.
If you need to trace & splice wires since the factory harness was cut, this guide should be helpful:
Pelican Technical Article: Changing Your Boxster Stereo Head Unit / Installing Boxster Ipod Integration - 986 / 987
That being said, if you're still set on getting a Becker, I have a CDR-220 for sale