The relays control the analogue outputs. As they click into action, that should be seen as a positive step forwards.

As you can generate test tones, I would say that the output card works, along with the DSP cards and FICL card.
It sounds like the input cards may still have problems...

Strip the unit so you only have the digital output card, DSP C/D, DSP E/F, FICL and CPU card.
Add the digital input card and test, then add each card back in turn.

I've had a unit where the tuner card kills all sound, so could be a single card that pulls the entire bus down.

Good luck, a logical approach should produce results.

Once you've isolated the faulty card(s), you can start to source replacements.

Cheers,

Steve

Main: 861v6 (LPS), 808v6, UHD722, DSP8000SE Anniversaries, DSP5200.2HC, DSP7200.2, SW1600, Sky Q, Cambridge Audio BD, Roon, M80
Office: 861v4 (LPS), 818v3, 800v4, HD621, M&K S150P, DSP5500HC, M&K MPS2810 sub x2
Son's system: 861v4, HD621, DSP6000.2, DSP5200HC, DSP33
Spare: MCD, 100 Series, 200 Series, 500 Series, F80s, C15s.