I looked at the manual before posting and it does not explain.
The problem is that the HD HD621 coax outputs are labeled 1/2, 3/4, 5/6, and 7/8
The Meridian configuration software shows"
DL/R ---> D4
DC/LFE ---> D5
DSurr ---> D6
There is an indirect reference of the L/R = 1/2
So one can GUESS that 3/4 = DC/LFE
and that Dsurr = 5/6
But nowhere is this stated in the Manual, I would be guessing.
The problem for the OA 13 cards remains. This was not an issue with the older configuration program that clearly said: OA 13 #1, OA 13 #2, OA 13 #3, OA 13 #4
This whole goofiness with 1-2 and 3-4 makes no sense in the configuration program. It should say exactly which one.