I have freepbx installed on a proxmox VM. It includes a Channel Bank driven via a Digium TE205P PRI card. Even with pci passthrough, the dahdi_test results are mediocre (99.2%) even though voice calls sound quite acceptable.
Googling around, I came across Dahdi dynamic spans, and set up a pair on another proxmox machine between a VM pbx and the host pc. Dahdi on its own was installed on the proxmox host, and connects to the PRI card. Both T1 connections to the Channel Bank are good, but they obviously cannot see Asterisk on the VM.
What I cannot work out is whether its possible to bridge the pbx dynamic spans to the “real” hardware ones on the proxmox host. Its a pretty obscure area, so if this query is met with deafening silence, I wont be disappointed!