Hello, I can record directly to an external hard drive using FireWire 800 port? I mean the RM32AI.

Yes, it's possible. But you'll need to make sure that your computer is also connected to the mixer via firewire 800. You can't connect only the hard drive to your RM mixer without a computer and record directly to the hard drive. What we really recommend is connecting a hard drive directly to the computer via a USB 2 or USB 3 connection, as it'll take some of the strain off of the firewire bus.