I'm quite sure there is deleterious interraction between plugged-in sources. However, the thought of fiddling around among a congested rat's tail of leads behind the pre-amp every time I wanted to listen to the radio, CDP, record-player or TV/video fills me with horror.

I'd gladly forsake a little quality for the convenience.

Mind you, having a separate pre. for each source, as has been mooted,(and separate amps, and separate speakers). Now, THAT'S something I haven't thought of!