mate going by what you just said it seems you're doing everything right. Red rock crabs are definitely the #1 bait and you're getting them so no problems there. Urchins are the #1 burley and u got that covered too. Maybe the area ur fishing is overfished??
Id ditch the snapper lead and go with a light running sinker - depending on swell. We generally only fish calm flat seas for groper which makes this style of fishing easier - the fish are usually right at ur feet. Again, Id go 24kg tortue...80lb is crazy IMO...still thats just personal preference but i cant see how u can cast 80lb very far if thats what ur trying to do? Another thing, fireline aint the best in the heavier line classes so ill ditch that in favour of tortue.
As for the bait, i thread it through the 2nd leg from the back and push it towards the claws. hook point is supposed to come out through the gut section and be a little exposed (3 ormm or so) and I use a 4/0 big gun rather than a 5/0.
If ur getting the smaller browns then the bigger blue will be there too...if not, keep moving around..if there are any big blues around they will take your bait first...no doubt about that! Look for ledges covered in barnacles, etc that drop straight into deepish looking water....its only a matter of time mate.
Cheers