I know of a couple of companies that mod DACs and source components but only one that, for certain, mods amplifiers - Musical Concepts (www.musicalconcepts.com). I have never used their services so cannot comment on their reliability or quality. Dan at ModWright is becoming a highly regarded expert at modding eletronic components. At the moment the only official mods, according to the website (www.modwright.com), are source components. But you might give him a try anyway.
