Now I purchased a mini PC with i5-6200U and 6x i211AT NICs...and no joy.

Running KVM and NIC passthrough, along with using pfsense/opensense works flawlessly on the new system...also only CHR v7beta8 has the drivers, but is not for production.
Please update/backport the intel drivers in V6 stable&long-term to a newer version, supporting chipsets like I211AT
Thank you very much for considering my request.
regards,
fred