I have just used ADAT to send audio from an RME Fireface 800 ADAT outputs to the H8000-FW. With a sampling rate of 96 KHz and since ADAT uses multiplexing, channels 1,2 and 5,6 carry the same audio signal. Also channels 3,4 and 7,8 again carry the same audio signal. It is my understanding that, because of the inherent limitation in the ADAT format, you can only use 1 channel of ADAT when using 96 KHz, since the H8000-FW only has 1 ADAT output. If you use 48 KHz however, you can process two channels, i.e. ADAT Channels 1, 2 will be processed from DSP A, ADAT channels 3,4 will be processed from DSP B. The processed outputs appear at the ADAT outputs (and also Firewire and AES). I have included a snapshot of my routing for you to get an idea.
Does this help?