Old organ level problem. Need help

[the19thbear]

I have an old organ.
It distorts too much when I hold down more than one key. The problem is that the amp ic's (TRA730's - summing amps) get overloaded at the input stage. I have had the same organ before and had the same problem. And I have listened in at the input stage and the audio signal is fine there.
I would like to attenuate (preferrable variably with a trimpot) the signals before they enter ICu1 and ICu2.
How would I go about that?
I assume that I can't just have trimpots between Cu3 and pin 14 and Cu17 and pin 11 on ICu1, and a trimpot between Cu27 and pin 11 on ICu2. I'm a noob but think this would cause impedance problems? And it might filter the audio as well, since my limited knowledge tells me that resistor+capacitor= some sort of filtering. I don't want to filter the sound, just attenuate it so it doesnt distort on the input side.

Or maybe there is another way of lowering the signales before they hit the input stage?
I' a noob be gentle and explain things thoroughly.

Thanks :-*

EDIT: The schematic was added twice. Don't know how to remove just one.

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[blue hell]

[blue hell]

The spots for trimmers you suggested .. before pins 11 (left in) and 14 (right in) seems fine to me - as in that it should not color the sound much.

Is it also distorting when you have a low output level? If so, it would probably distort in the input stage indeed .. anyway .. the volume control seems to be VRµ1 and VRµ2 .. when it does not clip inthe input stages of the TCA730 .. adjusting those pots may help .. but i think one to be on the front panel .. tis not super clear ...

I've found a datasheet for the TCA730 at : https://www.robkalmeijer.nl/techniek/electronica/datasheets/t/TCA730.pdf - it seems to be at alldatasheets too (but that site is a bit of a nuisance 9almost more hiding then publishing)).