I've trawled the forum gradually over the last few months for some definite answers on how to convert my HK equipped car to use a standard head unit. The original head unit has packed in, all speakers are waaaaay past their best and the amp is fuzzy as hell so I'm left with no choice! I don't want to go ripping the car apart as most of the wiring is there and I hate chavvy looking audio installs.

I've looked at the wiring diagrams and it seems to me the only difference between a standard system and the HK one is that the latter uses 4 line level outputs and a common ground, instead of having 4 separate earths. My plan is to use a 5-ch amp as per standard but will I have problems using a combined ground? If not this should solve the problem of having to run new cabling. If it is a problem is there a way around it?

Next question is that I have two similar looking round connectors plugged into the original head unit. The black 8pin connector is for the CD changer, but what is the light grey 6pin connector for?!

 

That's the low level output.

If you check the wiring diagrams, on Figure 18.1 the amplified outs are on IC1-6/7/8/9/17/18/19/20. On Figure 18.2 - the low level outs are on IC34-1/2/3/4/5.

On the components page for 18.2, IC34 is described as "6-WAY DIN / SLATE".