Passthrough behind PCIe-PCI bridge or how to forward PCI devices working through PCIe-PCI bridge?

Question

Xen

I'm trying to forward old PCI hardware (ProTools Mix) via XCP to a guest Windows XP. It works, but not completely. The fact is that on motherboards of the latest generations, PCI buses work through the PCIe-PCI bridge. If I just forward the hardware, the system sees them and you can install the drivers, but the ProTools program itself crashes with an error. All devices cannot be forwarded - only the bridge is forwarded. It seems that the devices are conflicting somewhere. But here's how to defeat it - knowledge is not enough.