Hey, by a total stroke of luck I determined what those opamps are:
"E53" is short form for "OPA 2353", dual, single supply (+5V), rail to rail, CMOS opamp.
Interesting, good find!
So, if I had to guess I say this unit runs at 5V completely, both analog and digital stages. And I would also guess that mods could not help much. It is *very* hard to run good audio at 5V. It would be much nicer if the unit stepped up to something like +/- 9 or even +/- 15V though...
Did you find the opamps that do the ever present 14 dB (or so) of gain?
I am trying to find out more about the signal path, especially the part(s) before the AKM 5365.
If we could mod the gain down (or up?) a bit that could help, depending on your situation.
[edit]
Hmmm! I see one E53 near the 1/4" jacks. (picture 10, left of the 1/4")
This opamp is dual; so where is the other one? (if it is the one for the ever present 14 dB gain)
Is it on the back side? (near the switch chip MAX4652)
Maybe we can confirm from the gain setting of the opamps these are the ones?
Also: where are the voltage converters to go to 5V from 3.7V of the Li-Ion?
Are they on the MT-PCB or on the small battery PCB?