I've got an MR816X. I'll double stress the 'only use a TI chipset FW card' mantra. The 816 is pretty flaky on a non-TI FW card in my experience, but rock solid when using a good card. Also, don't daisy chain it with other devices - give it it's own card for best performance.
This is the one I use: Newegg.com - ADS Tech PYRO PCI 64R2 3 Ports Firewire PCI Card Model API-315