I am using an RME RayDat
http://www.rme-audio.de/en_products_hdspe_raydat.php cost me recently about £500 in UK and allows up to 32 channels of ADAT audio (I have a Mac Pro so its a PCIE card). If you have no on board MIDI I/O it adds this as well.
Obviously the trade off is that the D8B audio is limited to 44.1 or 48khz audio but I am not sure how big a deal that is anyway. I am not running Abbey Road so its good enough for me.
I am using Logic plugins on the audio and routing out of my Mac into the D8B. Not sure what your D8B has but mine has 3 OPT8 cards which are routed to the Tape I/O banks (the second fader layer). So I can route analogue I/O (such as keyboard modules) into the first fader layer.
I am not using the D8B for audio conversion, I am using a TC Impact Twin into my Mac as I only record 2 channels at a time and am using the interface for monitoring, taking a feed via SPDIF out from the D8B.