Roger, unless I misunderstood what’s been written here—and it may also be true that there are differences between older and newer dCS pieces—I don’t think an external clock like the Mutec replaces the internal dCS clock. The Mutec, or any other external clock for that matter, is only going to improve the sound if it helps the internal dCS clock become more accurate. Here and here are two of the posts I am referencing. @James’ posts in particular have been very educational for me. Things I had taken for granted, or simply misunderstood, look quite different to me now.
Additionally, as noted elsewhere here, Bartok only has a Word Clock input, not a 10mHz input such as the Mutec Ref10 would require. So it would require an intermediary Word Clock like your 3+ or a dCS clock.
Before I went that route, I’d invest as much as I could afford in the highest dCS tier I could afford. As has been said, they’ve been at this for a few decades, and they’re the only ones who actually know the complete engineering innards of their DACs and transports. There is a reason that dCS clocks improve dCS audio devices. Mutecs and Cybershafts alike have excellent specs. But it doesn’t necessarily mean they will make one’s dCS component better. Just my two cents.