P38A Audio query (SW Wales)

Bit of a tale of woe here. I bought the P38 a month ago and found there was a loud crackle on the left channel of the sound system. Various people said it was likely to be a faulty DSP, so I got a s/h one from an eBay seller. I've fitted it and the crackle has now gone, but the CD isn't working, and there's nothing coming from the rear speakers and subwoofer. It looks like I have bought the wrong DSP - the original was a XQK10022340, and the one I bought was a XQK100210. The seller said the only difference was that the 210 would not run the satnav, but since I don't have satnav I thought it didn't matter. I now learn (from a different eBay seller) that the 210 is from the Discovery and will only run the radio and cassette, not the CD player. Trouble is, it's the CD player that I want most of all - I have no working cassettes and I don't often listen to the radio.

I need to return the incorrect unit, but the seller is 'away' so that might take a while. In the meantime, I can get the correct 340 unit, but it's going to cost around £400. I'm not sure if I want to throw that amount of money at it, to be honest. Might it be possible to have an audio specialist fit me a new head unit and wire it up to the door speakers and sub just like a normal installation? It's way beyond my capabilities, but surely someone could do this. If so, is it likely to cost more than a s/h DSP from eBay? I don't really need premium sound, just something I can play music on. I've got a cheapy 2-speaker unit which plays from USB in my other car, and I am fine with that. In fact, I now prefer USB to carrying round loads of CDs.

Any ideas, thoughts, guidance? Also, does anyone know of a good audio installer in West Wales who might be able to help? Every one I have called so far has heard the words Range Rover and has then made an excuse and left

Sorry for the long post.