From what I know, that’s not really possible, there are hard limits to how many PCIe devices can be connected without a PLX-style switch, which would increase cost.
On the Talos II, the six PCIe endpoints of the first CPU are used by:
- BMC
- USB controller
- NIC
- Storage controller
- PCIe x8
- PCIe x16
I imagine a Blackbird has the same configuration, although there additionally is audio-output; I imagine it might be through the BMC, which acts as a 2D GPU.
If you want to look at the Talos II diagram, you can expand this quote: