Take a look at the mamiya 645 afd, afd2, afd3.... those are the ones with the [semi affordable] digiback compatibility that you may want. Consider also the PhaseOne cameras, which are very similar.
But I would encourage you to set the digiback thoughts aside and just shoot film, and if you absolutely must have digital output, then have your best shots scanned as needed. For b&w work this is an especially good idea; there is no digital option that quite hits the mark as well as b&w film. For colour I wouldn't argue so strongly, but for b&w, film is indisputably tops.
The contax 645 cameras are truly great pieces, but alas they are made no more, so the most recent mamiyas have passed them up in terms of many capabilities. But, hey, if you're going to shoot film then who cares.
My current favourite of the 645s is the mamiya 645 pro, which is very modular. Take off the winder and the prism and you've got a cute little box, great for walking around with. Put on the prism and winder and you've got something approximating a big 35mm slr. I dunno about putting a digiback on it though, I wouldn't do that. For that I'd just bite the bullet and get the newest afd money I could afford, or stick with a good 35mm dslr for the digital stuff and save money. Fortunately for my bank account, I'm not all that interested in MF digital at this point

I just scan film shots every now and then if I need to.