Using adat for all connections to and from the H8000:
Can I have four channels of audio through the D/A's from Adat In at the same time as four channels through the A/D's into Adat Out, also at the same time as two channels to each of the DSP's also via adat? (i.e. 8 ch's of adat to and from the unit).
I assume you are referring to the H8000FW. The answer would be No. There are restrictions on the use of analog in and out – they have to go through the "Main In" and "Main Out" connection blocks. This means that you can have 4 analog in going to ADAT out and 4 ADAT in going to analog out, but this uses all the routing capacity, so you cannot also route to the dsps.
You could do what you ask with AES or FireWire in, it is analog that has the restrictions. If you have not already, try the Routing Utility – this will show what you can and cannot do.