Does anyone repair the dsp amp I've had two off these now costing a fortune

They're generally not repairable, but Marty is working on a replacement. Have a read of this thread
There's a guy on another forum who's looking for failed DSP amps with a view to repairing them. No idea if he's had any luck though.

In a word... No... they aren't repairable.

That's as a general rule of thumb though, as it would depend on what's actually wrong with them.
The guy on the other forum hasn't come back shouting from the rooftops that he's managed to fix them so far, so my guess is that they either aren't repairable or he's still working on it.

The failing DSP amps is the big reason I started looking into making a replacement system with used standard RR door amps on a board to then swap out the DSP amp and get proper audio working with the factory head unit. I did a writeup on the idea here: DSP Amp Replacement

I am in the process of building a couple of replacement amp boards at the moment - I now have the final connectors and pins here to finalise the wiring looms. I am still working on the factory sat nav integration though, but to get standard audio from the head unit is easy..

many thanks ive read through your wright ups sound complicated to me on mine ive got the sat coming through but no cd/radio/tape sound

The install of the replacements aren't difficult - it's just a large number of wires to solder together! I plan on offering a fitting service aswell for those who aren't as au-fait with a soldering iron, or don't want the hassle.

But that aside - if you only have the sat nav coming through, but nothing else - maybe try disconnecting the sat nav unit, and seeing if you get the rest working. I've heard before of the sat nav unit failing where it effectively permanently sends the 'mute' signal to the DSP amp for when it talks. If you get the radio/CD audio etc without the nav plugged in, then chances are it's possibly not the DSP amp that's at fault