So in summary you can alter the powder burning rate to increase the port pressure, or go to a faster burning powder to lower the port pressure. You can increase or decrease the weight of the buffer and or carrier to change the amount of inertia that must be overcome to unlock the bolt. You can change the spring rate of the return spring. and you can change the gas tube to increase/decrease the amount of metered gas available to operate the AR (gas block, Pigtail, etc.)
I'd start with cheapest modification/experimentation first - does it run with supersonic loads? can you try another powder - slower at first to increase the port pressure. Heavier bullet loads...
