Hi would just like to add my name to SVT services of Edinburgh .
Great service and gave discount when mentioning Lexus owners club !
Was a tricky fix as had intermittent no sound to speakers , so wasn't convinced it was the amplifier - anyhow bit the bullet and sent it off to Chris at SVT , he is not a great fan of the Mark levinson amp , but was diligent in replicating the fault conditions and eventually found the problem.
Now re installed in my face lift LS430 and sound is back to normality .
So if you have sound problems and suspect the AMP I recommend SVT services .