Hi Steve ,
Well, I owe you one. As usual

It looks like I'm saved....
....just.
So, I connected a single digital coax out of Meridian 800 (D1) and connected this to:
D4 MD2 on IE44.. No sound. Nada. I checked and rechecked. D4 is dead

So with a heavy heart, I then moved on to checking D5 instead. Omg..... SOUND!!!! Oh thank god. All I needed was one to work.
I then moved to check RJ45 out of HD621 into 861v6's MMHR RJ45 input (using a cheap ethernet cable) ..... SOUND.
Yahoo !!
Thank goodness..
I don't think I could have tolerated a firmware reflashing(risk) or, trying to buy/replace or reseat this card.
So, this all means I can have my cake and eat it too which will be:
- HD621 for Bluray using RJ45.
- 800 set to upsample, for DVD movies into the 3xSPDIF MD1.
- 800 Aux output (not-upsampling) into 861v6 (D5, MD2) and the latter will apodize and upsample = for Redbook CD.
I'm all sorted.

Thanks again for pointing me in the right direction buddy.
You're a saviour.
Oh yeah .. it's New Year's Day now where you are so... Happy New Year!!!

!!!
Andrew