Interfacing RME fireface 800 with Lexicon MX400

I'm going to use these two devices and the Lexicon manual mainly refers to using a MIXING console. Has anyone used these two together and if so, how did you cable it and how many ports must be sacrified on the RME fireface 800 to achieve the results?
Thanks
Steve

Quote below, from RME

As the name implies, the Fireface is a Firewire-based interface; and in addition to being RME's first stand-alone external Firewire device, it's also the first Firewire 800 (IEEE 1394b) interface on the market. This doesn't mean, however, that you can't use the Fireface with a Firefire 400 (IEEE 1394a) interface: the Fireface is completely compatible with 1394a interfaces, and, in fact, the unit itself is supplied with a Firewire 400 cable. For this reason, since Firewire 800 is backwardly compatible with Firewire 400 anyway, you might be wondering why the Fireface being a 1394b-based interface is so significant. Well, in keeping with many of RME's other products, it's possible to connect multiple Firefaces to the same Firewire buss — up to three, in fact — but only Firewire 800 offers the necessary bandwidth to do this. So, in a nutshell, if you'll only ever want to use one Fireface, Firewire 400 is fine; if you want to use multiple Firefaces, you'll need to use Firewire 800.

Mel