Kind of a late response, but here are the basics of my setup (maybe I'll publish some specifics in a gist at some point): - Hardware (which is dated now): Asus

Kind of a late response, but here are the basics of my setup (maybe I'll publish some specifics in a gist at some point): - Hardware (which is dated now): Asus Z87 Pro with i7 4770, 16 GB Memory, 4x AMD Radeon 6450 cards (< $20/ea used) - Proxmox/host config: vfiobind the PCI device IDs for graphics cards on boot, slightly modified pve-q35.cfg (workaround for some OS X issues on q35), using fairly standard VM args for booting OS X - GPUs work fine after a standard OS X install, but to get audio working over HDMI, I needed a couple of edits to my DSDT (basically just inserting a GFX0 device with "hda-gfx" = "onboard-1", a standard HDAU device, and a DTGP device), and boot with the Enoch bootloader (this can be specified in the VM args to avoid having to install to disk). No extra kexts needed. That's about it. Some of those things may no longer be necessary in the latest version of Proxmox (I haven't updated my base system in a while). Once I got things working, it's been completely stable for more than a year.