First off you need to create a 5.1 setup in the "I/O Setup" window. There should already be a couple of default 5.1 setups in the window. This will output each of the discrete outputs to an output on one of your 888s. Take the analog outs to the ProControl's monitor inputs. I can't remember off hand which these are but they are listed in the manual. The digital outs you'll probably want to take to a DA88 or some other multi-channel format for mastering.
You will need to switch the mode of your ProControl to "Surround" from "Stereo" in the utility pages. You will then be able to adjust the monitor volume for each of the six channels by using the pots on the monitor section as described in the manual: Stereo pot, Headphone pot and Cue mix pot. A bit clunky but it works well enough.
Bass management is functional, if rudimentary. A new and useful tool is the ability to assign a channel to more than one output at a time. This means you could for example assign you output stems to outputs 1-6 on your 888 as well as to say outputs 7&8. This results in your surround mix on channels 1-6 and an equivalent stereo mix on channels 7&8.