Let me talk to him; he may be amenable.
The latest mod I saw him do this week was to use a separate outlet for the XP-25 and that shaved off another 3dB of hum (as always, testing and adjusting at max preamp again, about 100dB total gain; he places the SPL meter on a mini tripod and points it right at the woofer); apparently, there is hum seeping through the XP-25 power supply from other components (digital, he says), hence this improvement. He now claims that at 66dB gain on the XP-25 - the level he uses for his A90 - he can barely hear any hum at max preamp gain, and he has, thus, switched to experimenting at 76dB gain on the 25 in order to lower it even further. Apparently, he has a lot of time in his hands, and claims that with all mods, he's been able to attenuate hum by 30dB (again, at max preamp again) - not bad and really what a bad boy the XP-25 is OOTB. With respect to hiss, he claims major success there too, and compares the used input versus the unused one on his XP-25 in this video he uploaded the other day
http://www.youtube.com/watch?v=eqTcdHdEefo - it looks like the results are quite evident even through computer speakers, and really stunning in person...