I need an audio interface...

Hi everybody!

I already asked this question over at the Final Cut forum - but I think it's better placed here...
I'm working with Final Cut Pro and Sountrack Pro with a Blackmagic DeckLink HD Extreme PCIe on a PowerMac G5 Dual and I often need to digitize 8-track DTRS tapes via a DA-98. Currently I slave the AES/EBU outputs from the DA-98 through a DVW-A500P to get the audio via the DeckLink card into FCP. The DVW-A500P only has 4 AES/EBU inputs, so I need to digitize my tapes in a 2-pass, time intensive process. I'd also like to be able to output at least 6 tracks to monitor 5.1 sound.
Since I'm using a FireWire 800 RAID would I need a FireWire interface card when the choice falls onto a FireWire audio interface to connect either the interface or the RAID to it?
Is there an audio interface available that would fit my needs?

I know these are rather "huge" questions but I'd greatly appreciate any help you could give me. Thanks in advance!

Regards,
Ingrid