Is there any obvious damage to to piston it's self? Detonation or preignition will usually cause damage to the piston it's self or the cylinder head before breaking rings.
Are the ring lands deep enough to allow the rings to properly compress? As in are the rings the ones called for by the piston manufacturer, there has been a lot of talk about using pistons for other engines to increase displacement, not a bad idea when you can't get what was once available, but different brands use different engineering specs. I guess what I'm trying to say is that there could be many reasons for a broken ring and detonation isn't the most common, might be time to start to consider looking any and all possibilities.