Finally got round to fitting my amp and sub and wiring in the rear speakers.
WOW!! I must admit, I thought the Concert sound system was good with the OEM amp/sub. Buy my god! Minimal bass on HU for the standard speakers and I have the amp on approx 50% bass for the sub and it sounds much much better!!
Pleased I went down that route now.
So now I have an Audi Amp/sub, Concert HU and compatiable Panasonic CD changer for sale.
THanks for everyones input and help in previous post.