Got these mics today and the circuit board is a little different than the A51 model due to the pad and lo cut switches. Still plenty of room to work but I'm not 100% sure I want to mod them now. They actually sound really good as is. Also surprisingly well matched within .5dB in an informal test.
Used them to record some acoustic guitar, mandolin and electric bass (on a 18 inch Eden cabinet right on the grill) and the tracks sounded really nice with the Aerco, the Grace V2 and even the mushy preamps in my Focusrite interface. Guess I'll take them out for an ontage ORTF jazz recording before I make the final decision.
The only thing I think that would really benefit is that the seller of the mod kits claim that the components are closely matched so for stereo applications they would be better but I don't know if I'm really buying that they match components in a <$20 parts kit - they are probably just saying that based on closer manufacturer tolerances from companies like WIMA, Nichicon, etc....