Don't know where you are located, but in the US....
I've had several NAD pieces redone by Peter Williams at Quirk Audio.
Excellent, honest work.
I've also bought a redone Hafler DH200 from Vince at Audio Proz. Did a fine job on it.
Either place should be fine.
I too have had great experiences with both of these fine folks (in fact, I use them both for different gear & depending on where I am at the time. And they are the only 2 people I ship my stuff to).
Peter @ Quirk Audio has had all 6 of my NAD 2200's and my 2 NAD 2100's (I wouldn't ask anyone to do those ever again, they turned into a problem to get done, through no fault of who was doing them).
Both Peter & Vince have each had my all of my other various gear at one point or another, except if there was a tuner alignment involved.
If you have made arrangements to have your gear tested with Amirm after the work is done, Peter @ Quirk Audio is a lot closer to Amirm & it makes sense from a shipping view point for it to go from him to Amirm & then to you.
Your location & the shipping cost is more of a deciding factor than anything, unless there is something special that you are doing (for example, you are getting something done with a receiver that has a tuner or a tuner, well Vince @ Audio Proz can do an FM alignment. To my knowledge, Peter doesn't do that. But, since I haven't needed one in a long time, that may have changed).
As to the quality of work, you can't go wrong with either of them.
