Speakercraft MZC64 + BB50S - how many speakers can it power?

I have a MZC 64 and BB50 powering 12 x AIM 7 TWO in-ceiling speakers. The system is currently powering 4 zones total, 12 speakers, with 2 additional line level outs that go to separate amps/receivers. I had a vendor do the complete install a few years back and am considering expanding to add 2 outdoor speakers (Speakercraft Ruckus), but on an existing zone. The new vendor I'm talking to feels I need to add another BB 50 due to the 2 additional speakers I have, but my gut feeling is that I have enough capacity. However I don't know how to objectively calculate this.


I've never had any issues with overheating, clipping etc. so feel I have plenty of spare capacity.


Any input would be appreciated!


Thanks!