Relay based audio attenuator? Interesting, sounds like acoustic noise is acceptable.

Split your ground plane between audio and control circuitry. Their grounds meet at the supply.

A low power controller that integrates enough flash to eliminate an external "data bus" and allow use of all 4 ports at the lower "switching rate, & provides a serial debug capability is where i would start. I would suggest looking at a Atmel '2051 (or like) part.

If you didn't use those Op-Amps i would have guessed you wanted to build a "dry", passive bi-lateral attenuator.

Since you use Op-Amps did you reject using switches like the SSM2404? Or, are you familiar with the LM1972 type switches?

regards,
p


SSM2404:
OFF ISOLATION 10V rms, 20-20kHz - 120 dB
CHANNEL-TO-CHANNEL 10V rms, 20-20kHz 96 dB
THD 0-10V rms, 20-20kHz - 0.003%