Nice buy on that CN9-A, that one is on my buy list soon to run 3xSRM6 + energy build,
It is too bad the energy is all in the CT, so you only get 2 critical slots for 2 hardpoints.
2 x MPL (2 crit, 4 tons, 12 damage) would probably be the best punch for the crit space and tonnage. Runs hot though. (I run 2ML and 2MPL on my jenners now)
A LL is 2 crits but at 5 tons(9 damage), and a LPL is 7 tons(10 damage). Can't fit a PPC in there.
With that type of loadout, sounds like you will forego your ballistic hardpoint? Even a token MG will take 1.5 tons. Almost better to spend that on a CASE and an extra ton of SRM or a heat sink. Or upgrade with a AMS.