Took your advise and opened a support ticket. A few actually....sorry Pokeys guys.
To answer my own question. No, Pokeys 57cnc only has 4ch active. The 5th, 6th, 7th and 8th on the card are not so usable with Mach3.
However, via my support tickets I have been informed that the Pokeys team is now working on implementing the 5th and 6th axis control (pulse engines) and will be updating the Mach3 plugin within a few weeks.
This is great news! Mach3 runs up to 6 axis and having a card like the 57cnc to control those 6 axis will be a nice feature.