all those ring failures do suggest you are having problems with detonation. cast rings are brittle and the shock waves caused by detonation will crack them. then they will overlap eventually in the grove and crack the piston headland. trying to find rings that will survive the poor tune is only a band-aid measure, and the detonation will eventually damage some other component - like pistons or big ends.

Controlling detonation means controlling boost (within the efficiency of the turbo), mixtures, timing, and temperature - both inlet air temp and coolant temps.

Also while the head is off, smooth all the sharp edges in the combustion chamber with an emery flapper wheel. a sharp edge (or particualrly a point like you find in most peanut chambered heads) can be a hot spot causing detonation.

ACL, Grant and the other aftermarket piston/ring manufacturers do not list moly rings. Their "Chrome" rings are chrome plated black (cast) rings. these will be no more durable than normal black rings.

Chromemoly rings might be available from Nissan, but the standard cast pistons are a weak point too. Really you should be getting forged pistons made up, and in that case I'd go and research suitable moly rings and have the piston made to accept them. A slightly cheaper alternative may be to search the Wiseco motorbike piston catalog for a suitable piston WRT pin, bore, deck height, and head profile. Alot of these are forged and come with moly rings.

Aiming for a certain target boost pressure isn't the way to go. 14psi doesn't mean it will make more power than 10 or 12psi for example. A well designed setup (manifolds, suitable cam, good flowing head) will make more power at lower boost than a setup with inherent design problems, and simply trying to overcome it with more boost. It's highly likely that the very small turbos you are using are producing more heat than anything else at those boost levels.