I happen to know Pauls Dad (Paul senior). He was never a CB until he went to the States so he can play other parts of the pitch.
In terms of the difference of the difference between the A League, S League and ASBP, didn't a few Auckland guys go over a couple of years ago to have a crack? Mulligan, Coombes and Butler? They didn't get in but if you accept that those 3 are in the upper tier of ASBP players and not one of them caught on (and we can only assume on playing ability rather than anything else) that would suggest that the S League would be a step up from ASBP.
Cunningham has had a sniff with the Phoenix but that was under Ricki. Paul is 27 so I'm not sure he is a player in the age range we would look at?