ok, thank you John for your explanation!

i missed it was about 5.1 not 7.1...

Things i still not understand are these extracts from 861 V3 and V4 brochure:

"Up to 10 outputs at 96kHz/24bit "

"In each DSP core, the incoming signals are processed using a variety of proprietary algorithms and up to a dozen output signals are generated. These signals can be used to feed a number of speaker layouts, ranging from 2- to 9-speaker stereo/surround with
multiple subwoofers (with adjustable crossover parameters)."

So what can you do if you add a third OA03 or OA13to the first 2 used by the 7.1 output?

Epectaz
Mas de l’Issart (sur RV) (Saint Félix de Pallières) Pallières 30140