tommo, i'd make the decision based on whether you want the stock dimmer lights kept or not, cause that's a feature you simply can't get in aftermarket head units. i recall someone saying you could post it to phreddy and he will do it for you, so maybe that's a better idea if you want the dimmer, but otherwise, aftermarket head units are in almost every way better than the stock ones (assuming you have a bit of money to throw around).
If you want quality, you'll need a good HTL converter. Apparrently the good ones (as above) are a good $150. for that kind of money, you're better off with just getting a decent aftermarket one, and the adaptor to use your buttons.
However, as a general rule, the HTL converters are generally decent quality (i would rate them at about 96kbps comparing to mp3s) but some say they are as low as FM radio (56kbps, if you know what i'm talking about). As in FM transmitters like for ipods, distortion increases exponentially with bass boost and that kind of thing, so turn the volume up on your amps and down on your head unit to avoid that bottleneck. But for good quality listening, you're better off getting the mod (if possible), or a decent aftermarket unit with plenty of pre-out goodness
