I got quoted 15k which seemed a bit steep
Certainly not cheap in a vacuum but a good deal relative to buying a new pair, no? I've used Ayre's upgrade service before and I am a big fan of not having to buy a whole new unit to get the latest and best performance. In the case of the MX-R Twenty, I vaguely call reading a post by Charles Hansen saying that they pretty much replace everything except for the chassis and, maybe, transformer.