A better sounding 812 monitor module for an API 2488?

[pinebox]

Hello, I have been a repair tech for over a decade but my large active circuit design experience is minimal. One of my friends/clients has been asking me to make better sounding monitor cards for his API for a couple years now. I know a lot of people complain about the audio quality of these, and looking at them there isnt much to the card, just a couple ICs, relays, some routing switches and pots, so I am going out on a limb and assuming that the two dual op amps are mostly what is holding it back from sounding more like its channel side counterparts. The 812 module is half width a normal console channel, so fitting a 2520 to this footprint was limited by the height of the DOA, my solution for this is to face the odd and even modules towards each other and mirror them with a shared face plate just like the 528 module so that the blocks for each side have space between them to live. But perhaps I am putting the horse before the cart by designing the mechanical before getting thoughts on this circuit.

1)Would this circuit benefit greatly from swapping the 4739 IC with two 2520s or is the weak point a bigger picture than that?

2)What values if any should I consider adjusting around the 4739s if replacing with DOAs? Can I essientally swap them 1:1?

3)Could I put a single 2520 after the TAPE/PGM relay switch instead of two of them before the switch? Or is there a good reason for having the op amp previous to the switching?


Thank you anyone who shares their experience with me.