Fine picture, sound from all 8 channels, but the signal for the center speaker and sub is missing! Both speakers get the 'residual signal' from the respective DSP setting used, but the main dialog is gone.
[/quote] The reason for this strange 'missing center/sub' was the wrong connection of the three coax cables between the HD621 and the G68. Different to info provided earlier in this thread (#95260, 2009-06-04), the correct allocation to the MD1 section of the G68 is: 1/2 ->D1, 3/4 ->D2, 5/6 ->D3.
Now everything works and sounds fine.

My overall learning from setting up the HD621 is that it requires the Mconfig program and storage of the file with the correct settings via RS232 port on both the G68 and HD621. I my case there was no chance for 'plug-n-play'.

G68XXV, Oppo BDP83, Forsell CD, Audio Syn DAX-2, LG LSS-3200A TV box, Krell amps, Apogee Diva(M) & Duetta(R), Dunlavy HRCC(C), Audio Physics Virgo(S), Velodyne DD-15 sub, Transparent cables, Fujitsu LPF-D711 projec, Draper 10'screen.