Denon AVR-X1300W DIY amplifier

[XploD]

Hi all, I would like to present my planned project and see if can get some answers, ideas or corrections here So I bought this AVR broken for cheap, thinking that I can fix it. I was wrong. It's stuck in "Update retry..." error and there's no sound (MUTE is active). That's why I though I could fix it: I got the firmware and I tried to re-flash it via USB but it gets stuck at some point due to missing ACK from Audio PLD. I even tried to re-flash the EEPROM for Audio PLD with dump from a working receiver but no help, probably the IC is faulty.

But I have a case in almost mint condition (without a scratch) and working:
 - power supply with various voltages available
 - 7ch power amplifier with all the relays and protections
 - FM/AM tuner
 - VFD display
 - all the connectors, antennas, buttons, rotary encoders, IR receivers etc.

So I decided to start a DIY project. And before you ask, no, it's not worth it money wise because it would be cheaper to buy a new AVR but I want to learn something and create something myself. I was always into audio amps and I have some experience with Arduinos but mostly I'm a newbie.

The plan is to design my own board which will replace the original digital board of the amplifier and re-use all the connectors (internal and external ones). This board will contain:
 - ESP32 or something similar for controlling everything
 - Raspberry Pi Compute Module 4 running Volumio
 - ADAU1452 DSP (based on Free DSP OCTAVIA project) with all ADCs and DACs

The plan is, of course, to use ALL inputs and outputs of the original AMP except HDMIs (only one output will remain for RPi):
 - 2 optical SPDIF input
 - 1 coaxial SPDIF input
 - 3 analog inputs (+ one for FM/AM tuner)
 - 2 subwoofer outputs
 - (PHONO input - optional)
 - front USB for playing media
 - headphones output
 - (microphone input - optional, for room correction)
 - 7 fully controlable analog outputs for power AMP (with support for 2-zone mode)

All the pins that will be left unused (for either DSP, RPi, ESP32 or from the Denon itself) will be exposed via connectors so that I can later easily develop and plug-in other modules.

Currently I'm learning KiCAD and I already started slowly designing my own board, module by module. I'm also trying to identify all unknowns and re-solve them. I found out which IC is used in FM/AM tuner from Denon so my next step is to try to connect it to Arduino and get it to play something so that I know it works and it's controlable. I'm also meassuring voltages needed to activate all the relays, mute and other on the power amp board. And my biggest unknown currenctly is the VFD for which I have another topic here: How to drive FUTABA 18-BT-02GINK VFD

I will give my best to properly design the schematic, re-check everything multiple times, even ask somebody to take a look (for some money of course) before I produce the PCB. But my biggest fears is that I will eventually have problems with thickness, position or length for lines etc.

Feel free to give suggestions, ideas, corrections or to talk me out of that plan if it's too far-fetched for a newbie there's always a chance I will give up at some point as currently I'm at 0 cost, I'm just designing everything in KiCAD so my only (and most expensive) cost will be to order the actual board. The same company will manufacture the board, acquire and solder all the components for me so that's the only cost.