Both AMP50 and AMP100 can operate between 4-16Ω.
Assuming you are connecting standard 8Ω speakers, you can connect up to 4 speakers to AMP50 and 8 speakers to AMP100 using standard parallel wiring method (ie. daisy-chain).
Alternatively, you can utilize series and parallel-series wiring to increase the number of speakers you can connect to the amplifier. Please use caution and consult an A/V professional to ensure safe operation when wiring speakers in series or some combination of parallel-series.