Hi Andrew,

I would test each input on the IE44 card separately. Set each up as a CD input and try D1 - D6 separately. Test with a known good digital output and see what you get.
If D4/D5/D6 doesn't give any sound or signal lock (turn on Diagnostics displays), then I would suspect half of the IE44 card is duff. I would test the MMHR input too (any cat-5 cable will work to test it from the HD621) and see if that works.

It is possible that the inputs have been blown. It is very easy to damage a SpeakerLink input with a PoE Ethernet switch - 48v does not do SpeakerLink much good!

Lastly, it may be worth re-flashing the unit's firmware, re-typing, and re-configuring everything from scratch to rule out any configuration errors. You could also re-seat the card in case it has worked loose...

Otherwise, you'll need to speak to a dealer in order to obtain a replacement IE44 card or speak to the original seller to arrange some form of refund.

Good luck,

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.