The ACS override patch doesn’t actually change the groupings. It just changes how they appear to Linux.
This means that on an electrical level, the devices are still grouped and can communicate with each other. This can play havoc on stability.
For example: If you have two AMD cards in the same electrical IOMMU group and you apply the ACS patch, when you load the guest GPU driver, both the host and guest will crash because the GPU looks in the IOMMU group, sees the other GPU (for the host) and tries to communicate with it. Because the host GPU is running a different driver (Linux), they can’t properly communicate and they both get corrupt and crash.
For the record, it’s not dangerous in a permenant fashion, just dangerous as far as stability goes. While I don’t know enough about PCIe standards, protocols and protections go, I don’t think this could cause you to fry a device.
I’m using my Taichi without the ACS override patch, but I’m not passing through USB. I’d give a bios update a try first. Don’t use ACS override if you can help it.