I should have stated that the irreducible mass energy of the black hole increases by the mass energy of the original particles plus the rest mass derived from the gravitational potential if the particles interact on the way in. The black hole mass only increases by the original particle mass energy if they do not interact.

The mass of the black hole is irreducible unless you buy in to Hawking/Bekenstein radiation which is based on negative energy, whatever that is. Let me know if they ever find any.