I do not dispute what Tony and the other guys say, but as someone who does run the Empeg through their head unit, I'll add my 2 cents. As long as your head unit has an auxilary input, the quality will be very similar to what you would get from the CD player in your head unit. I wouldn't even bother if you would have to use a tape adapter or FM modulator.
Just a couple things to note:
I have leave the EQ and volume on my empeg flat-lined and control these through my head unit's EQ and volume. This means that you must use two remotes or adjust the volume and EQ settings by hand as needed.
This works out fairly well, because I leave them flatlined when in the house anyway as it pipes into my entertainment center's receiver and I use that for volume and EQ.
Tony is right though...since I got my empeg in January, I haven't touched the cd player and the radio has only been used once or twice.
I guess what it comes down to is if you can afford to get a decent amp and want to go through the hastle of installing it in a vehicle you are considering getting rid of.
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~ John