You could add an extra firewire card to your computer, then the FF800 and the H8000fw have their own firewire interface. It could work, however I had some problems with 2 Belkin Firewire 800 / USB cards, internal firewire and the H8000fw, Focusrite Liquid Mix and the Lynx LT-FW combination.

Another option would be exchanging or upgrading your FF800 to an Lynx Aurora 8 (I found it having more details than the FF800) and getting a Lynx AES16e card in your computer. This way you can connect the Lynx and the H8000fw over AES/EBU, it's rock-stable at 96khz. Should you need even more channels in the future, you can even get a second or third AES16e card (we have 2x Aurora 16, one Aurora 8 and the H8000fw connected this way).