OP-AMPS in Marantz PM7000 Amplifier

[Alex2]

Hello,

My name is Olek, I'm from Poland, and sorry for my english.

I have very important for me question/request about Integrated Amplifier Marantz PM7000 (or PM8000). I have PM7000 (and Marantz CD6000-after upgrade) and I want to change op-amps (Operational Amplifiers) inside to better ones. But I don't know which is responsible for what audio module/unit/signal_patch (I don't have any electronics and elements scheme or chart). I can see on the little plate inside (near the volume potentiometer/regulator) four op-amps (I think all are dual, for L and R channel):

1. 7501 - NJM2068DD (7501, 7502, 7503 are on the parallel board/plate to basis-ground)
2. 7502 - NJM2068DD
3. 7503 - .................. ?
4. .... ? - NJM2114D (it is only one op-amp on board/plate with the volume potentiometer/regulator, board parpendicular to basis-ground)

Which is to tone control in bas ?
Which is to tone control in treble ?
Which is to volume control ?
What for is the fourth op-amp ?
Maybe I'm wrong and their destiny and using is even different ?

Maybe photos with these op-amps will be helpfull: http://garmin.webpark.pl/pm8000.htm
(pictures nr: 7 - there are 3 op-amps, and 8 - there are 1 op-amp)

I listen only in Direct mode/patch (tone control and balance are disabled). Which is the most important to change for me ?
I want to change e.g to: OPA2604 or AD825.


I will be very grateful, much obliged and appreciate.
Thank you very much.

Best Regards
Alex2