first advice is *don't* connect a mic to the H8000FW inputs. Mics require a preamp to raise their signal to line level (+4dB). The Eventide inputs are not suited for such task. They need to see a preamped signal for a microphone.
there are 2 different aspects:
1 how the signal is routed TO the H8000FW inputs and FROM the H8000FW outputs
2 how the 2 DSPs are routed
The unit has a set of internal routings stored in it; you can access them by pressing and holding the PROGRAM key for a couple of seconds.
Again, I'm afraidSonar doesn't allow more than a single Firewire driver/device to be used. This may well be the reason why you get no signal from the system, using everything on FireWire.
all the best