I think Michael does something similar to the familar Scott Dorsey mod, and involves upgrading resistors, capacitors, and one or two FETs. Scott Dorsey's article was in Recording magazine, a back-issue that is sold out, but you can find copies on the 'Net, for instance, here.
I'm always amazed at those who can hear immediate differences in sound samples. They can recognize even the difference in microphone cables. I'm having much difficulty hearing the difference from the old mics. It's not that the sound is different; it's that there are too many differences. Let me explain.
First, I'm an old guy and like all of us old dudes we can't hear much above 10,000 hertz, so there may be a good deal of changes that I won't ever hear. Then there is the matter of my nails. A couple of months ago I filed them down and started striking the strings with just the finger pads. The same deal for the thumb. But while playing with the Gibson I started using a bit of thumb nail. Darn, it sounded good! So the thumb nail stays. Also I got some Mogami Standard cables with Neutrix connectors. Maybe that changes the sound. One last thing: have you ever tried to duplicate your sound from one session to another? I've read of people who go back the next day to splice in a correction and can't get the sound the same. Humidity, temperature changes; furniture is not in the exact same place; the butterfly's wings.
So if I can't tell the difference right away, no big deal. I think I hear more, and better, bass, or the bass is clearer in one of the recordings. It seemed kind of enormous and bigger than life, and made the guitar seem very close. I looked at some spectrum displays of the new versus old mics, and the new ones are picking up lots of well defined pitches down to 10 hertz. Unlike before, the levels are well above the everyday background noise from the local highways. I like this! Even though most of us have sound systems that cut out well above forty or fifty hertz, you can still feel the lower sounds, and it gives a sense of guitar / player presence to the recording. This probably requires some adjusment in mic position and maybe playing. As I use these more they will probably be other changes. I'll give it a while. In the meantime, I ponder this comment from Gearslutz.com about mic shootouts:
...I don't really like shootouts with all the mics in the same position. One should basically go for the best sound with each mic.And that seems to add just one more variable to an already impossible task of rating one good mic over another similarly good one.