Talk to Pupuke Robati at the wharf. Buy him some Heine's and pick his brains.
He knows those waters where you are for Yellow fin like no one else.
You need to get below the thermocline which is normally 90 - 110 fathoms (about 160 to 200m) to catch them consistently during bright daylight hours.
Up current edge of the FAD's is your best bet.
Don't use NZ style leaders, go much much lighter.
Sounder: either don't bother or you need a really good one as the bottom at the FAD's there are 1500 m deep which makes it hard to get a return signal, or you often just get a lot of noise.
Live baiting and dead baiting is much more effective than jigging in those waters for Yellow fin.
Your best information investment is $50 for a box with Pupuke. It gets very technical to catch them consistently there like he does.
Hope you are enjoying yourself :)