Ok now my system is coming along nicely I'm starting to think of what I can do next would a headunit such as a Clarion DRX-9255 have a noticable sound improvent over my current headunit (see sig) or anyother headunit with a 24bit D/A for that matter? I don't want to get rid of my current headunit as it plays Mp3s yes I know they are crap but they are bloody convient so what about putting the signal from a second unit into its aux input would the signal be degraded by doing this?

What percentage fo teh time do you spend listening to MP3, CDA, Radio.

If it's CDA only equals 10% or less of you listening time I wouldn't bother investign the extra cash into a new headunit.

However if you do listen to CDA a lot and fell the rest of your system is upto scratch the upgrade to the 9255 could provide some very nice improvements in SQ.

You don't want to be feeding a high end headunit a poor analouge source. The signal will not get worse but it won't get any better either. Personally if MP3 is a must, I'd look for a audiophile headunit with MP3 support, thre's plenty of them out there.

This is just for SQ competition (and to be different) mainly so the signal from say a 9255 to my current deck won't get degraded from my current headunit? is that correct.

Really depends on the preamp of your existing headunit.

Personally I'd run it the other way round, or just have one headunit installed and swap them out for comps etc.