High level and RCA inputs

I'm looking to install my factory cd player (high level output) and also an

aftermarket head unit (rca output).  I have a Rockford Fosgate amp that has inputs for both high and rca level inputs.  Can I connect both at the same time and what kind of behavior can I expect?  I don't plan on having both on at the same time.  Will there be any feedback or noise if both are connected, but only one is on at any one time?

Another way I think I can hook this up, is to get a line level converter for the factory unit then hook up both sources to a source switcher like the PIE MPSS-4, to the AMP.

TIA.

I would NOT connect both at the same time, to the SAME unit anyway. If you have two seperate devices, it may work, likek tehr head unit using the HIGH, and a DVD player using the LOW. The worst you'll get is noise or a 60Hz HUMM due to grounding issues. Try it, you can't really damage anything. Feedback (speaker whine) is only from MIC to SPEAKER issues, there is GROUND feedback in these applciations.