@Humbleminer: thanks, that's exactly what it was!! Now finally mining away with all 6 gpus for the first time!! Epic!
2 things though:
- vddc shows 1.2v in the web stats interface but max 1.14 in my conf file... And ccc seems to confirm max at 1.14.
- hashrate is 15kh lower per card than in Win8.1
Undervolting via cgminer rarely works. You can use MSI Afterburner in Windows in order to check if the voltage control is unlocked and can be controlled by software. If not - you'll need to flush you GPUs' BIOS in order to unlock. This is potentially dangerous since that might brick your GPUs.
As for the hash rate - you'll need to play with thread concurrency, engine/mem clocks and other parameters for your specific cards in order to find a sweet spot.