In fact, I'd recommend simplifying things even more when starting out. Try making just three measurements at a given listening position.Given the number of subs and listening positions you're considering, I'd recommend first doing a kind of trial run, with fewer subs and maybe three listening positions. In that way, you can gain some experience without the risk of causing an error that might invalidate a large number of measurements (78 in your case, and that's without any main speaker measurements).
- Frequency response of sub A
- Frequency response of sub B
- Frequency response of subs A and B together
Import these three measurements into MSO. Configure MSO to take the sum of the first two by making them a measurement group. Compare this computed sum to the third measurement above. If they don't match, something is likely wrong with the measurements.