Thanks for the feedback everyone.

OK, so I'm going to take the plunge and get a new HU.

Other than the obvious sound improvements, my additional feature requirement is bluetooth for phone (integrating with the factory steering wheel controls). I don't care about nav as I use my phone for the occasional map checking anyway but if the HU comes with it then that's fine.

Looking at either a Pioneer or Clarion unit.

Tossing up between:

Clarion VX404AU
Clarion VX603AU
Pioneer AVH-275BT
Pioneer AVH-X3500BTDAB
Pioneer AVH-X3600BTDAB
Pioneer AVH-X5550BT
Pioneer AVH-X5650BT

Willing to spend up to around $600.

Most of these units are listed on supercheapeverything.com for VERY low prices compared to the quotes I got from some stores today. Has anyone had any experience with buying from there? I'm not seeing a lot of info on reputation by doing a google search.