Hi Adam. I've got a 54M with Hasselblad V adaptor. Latest version of Captureshop (to my knowledge) is 6.1.2. On the back of a Hasselblad 500 EL/M I can shoot via Thunderbolt->800->400 adaptors in both Master and Slave modes with my 2013 iMac. However, on a P3 with CMV shutter (where presumably more communication is required), the setup won't work with the iMac - I can only get working with direct Firewire 400 connection on old (2007) Mac Pro tower.
I saw on another thread somewhere that someone had similar problems with 54H, P3 and newish MacBook ... eventually resolved as bad quality connectors in the adaptor chain. So it looks like can be done with current-ish gear. I'm hoping my problem is same but won't be able to spend any quality time on this for a few weeks.
Hope this helps.
Malcolm
Got a bee in my bonnet after previous post. Have finally got 54M back working with P3 on 2013 iMac running macOS Sierra 10.12.6 and CaptureShop 6.1.2. I think the Thunderbolt->800->400 adaptor chain can be problematic. Also found that one of my FireWire 400 cables that worked with the Hasselblad setup won't work with the P3, while the other does (guess which one I kept mistakenly using).
I don't have flash-synch with CMV shutter on P3 ... but also don't get flash-synch using same on old Mac Pro, so suspect shutter to synch-socket problem as time exposures are working perfectly - will have to open it up when I have time . This is old gear that's been standing for long time before it came my way.
Hope this helps
Malcolm
... Update - If I use a Y synch cable so that I'm connected to both lens shutter socket and synch socket on 54M the synch does indeed work. I think this is due to sharing ground from 54M so everything points to bad connection inside CMV shutter, i.e. synch socket not earthed, something I should be able to fix myself.