Aftermarket vs. factory head unit?

I'm upgrading my '07 Jetta HU to a JVC unit with preamp outputs. Normally, I'd know exactly what I'm doing in regards to the car audio hobby, but as this is my first time dealing with HUs, I was wondering what kind of difference the JVC would make over my factory unit. Especially in regards to signal quality both to the factory component door speakers, and the aftermarket subs which are currently running off a speaker level converter. Is it true the signal would be clearer? Especially to the subs, by using direct RCAs?



Also, it makes 20W RMS to each channel so would that clear up the muddy highs and AUX source alternator whine I hear at higher volumes? I will get a separate full range amp/speakers if necessary at some point in the future, just wondered what to expect from just an HU upgrade with factory speakers?Aftermarket vs. factory head unit?
I wouldn't anticipate a significant improvement.



There is no reason an LOC can't provide clear, strong signal for an amp. I'm not sure why the reputation for LOC's having poor SQ is so popular. My guess is a lot of people use the cheapest LOC they can find. A good one shouldn't degrade the signal at all.



As for power - I don't think 20w rms is uncommon from today's stock HU's, so it's possible you won't be gaining much in terms of power. My '99 Taurus produces 20w rms/ch, however, it uses an external amp.



I would be optimistic the alt whine you got from the aux input could clear up, but if you're plugging the new HU directly into the stock wires the problem may transfer from the old HU to the new.

I once cleared up some alt whine simply by disconnecting the stock HU ground wire, attatching a temporary extension, and trying various ground locations under the dash. It wasn't difficult to hear which ones worked and which ones didn't. Once I determined the best one I ran the wire neatly to the new location and made a permanent connection -- simple and successful troubleshooting.