Regarding your question, maybe it would be easiest to just start building the MB6582 baseboard (and e.g. populate it with a single core and two SIDs first) - it connects easily to the MB6582 control surface and all is well documented. As you were already thinking of going that way, i’d recommend to just do it. The MB6582 baseboard needs not be fully populated with PICs and SIDs, you can just start with a single core and a SID pair.
Thanks so much Peter, I now have hours of entertainment while I wait for the parts to arrive. That build guide looks great - thanks for all your efforts!