Basically faced that dilemma when I got my motherboard, as it only has a VIA-based single Firewire channel and I have two RME FireFaces, 800 and 400.
I ended up getting a couple of cheap TI XIO22013A-based x1 PCIe cards from SIIG and Syba, as I couldn’t run both FFs from one card for some strange reason, probably to do with the TI chip. They both run at up to 192k just fine.
However, the writing in on the wall for FireWire, with USB2/3 being prominent. I am just glad that I didn’t have to replace my FFs just yet, as I am waiting for AoIP interfaces with low IO numbers to start arriving, as that interface is based on Ethernet, is expandable from multiple vendors using the same single ASIO driver, and allows audio interfaces to be placed remotely wherever one needs using cheap network cables and switches.