Sound Channel Settings?

Hey all, i Have a HW-QC600 Soundbar, what should i have my channel output settings set to?

I have passthrough enabled, using eARC but the channel setting seems to change the sound and im not sure what it should be set at?

Currently set to 3.1ch that i think is correct, running on an N2 latest version.

Thanks.

Anyone? Cant believe nobody knows?