Is the stock, non HK system wired to accept a pre amp? If it is, and I add an amp I'm assuming this wouldn't interfere with the steering wheel controls. Am I right?

The delema is that if I go with an aftermarket head unit, I loose the steering wheel volume/switcher control, unless I go with a high end head unit plus some sort of $200 unit to make the controls work.

Is it easier to just add an amp to the original system? Will I likely regret not replacing the head unit because of it's quality (or lack there of)?

 

No pre-amp on H/K or non-H/K. You'll have to snag it line level.

 

Adding an amp wouldn't interfere with steering wheel controls. The OEM head unit doesn't have line out, but many aftermarket amps have both line level and speaker level inputs, or you can use a speaker level to line level converter box.