jasonmcguire,
Sorry to come (a few years) late to the party, but after reading your post, I just replaced the stock 5687s in my CD-77.1 with Bendix 6900s, switched from Digital Master II to I, and it's easily the most natural digital I've ever heard. Just ordered some Brimar EZ80 black plates to replace the stock Brimar-labelled gray plates, hoping for further improvements. Thanks for the tip!
Richard