Just to finish this thread. . ..a few months on and all is well..
I cured the whinney interference noise by re-running the positive power cable across the rear of the boot under the plastic where the boot latch is and across to the amp on the other side.
This way it is away from all the signal wires. Turned the gain down a little and the noise has now almost completely dissapeared and is not an issue.
The amp gets pretty hot but has not hit the thermal cutout yet, even after 5 or 6 hours of constant high volume.
So, to summarise, my car had standard audio and now has:
Logic 7 Tweeters in Front
Logic 7 Mids in Front
SWS-8X (2 Ohm) Subwoofers
Vibe Litebox 4 Amp powering front door speakers and subs
Dension Gateway 500 MOST Interface for I-Pod / Hard Drive control
Total cost around £650 - 750.
System sounds fantastic....Worth every penny.
Took some time to adjust the levels and get them right, but now have it all sorted and I am very happy with it.