On https://pve.proxmox.com/wiki/Pci_passthrough
Isn't explain how to isolate IOMMU.
Is a NUCi3BEH, that support 7.1, anyway is impossible use an external soundcard, because lost all channels, you can't handle 5.1, only 2.0, usb soundcard, have only 2 mini jack.
There isn't a way ? Is possible...