Sometimes a man can not figure things out, but in this case I first tried with the DVE BD-testdisc and found the same problem, so my attention went towards the cable between the HD621 and the 861v6 MMHR input. I switched to another cable, and the problem went away. The wiring in the cable looked identical in dim light, but who cares as long as it is working:)
Thanks for the help guys!

Regards Joern
Editor, Watt Magazine, Norway
Gear: JBL Array 1400, Array 880, Klipsch rs62x4, Velodyne DD18+, 861v6, HD621, Cambridge 752BD, Pana 65VT60, JVC DLA X75, SR 2:35:1 152", Prismasonic, PS3, Xbox360