Use this calculator to ensure you do not connect too many loudspeakers to an amplifier. When speakers are daisy chained together the wiring is in parallel and the ohms drop. Most modern amplifiers can delivery power down to 2 Ohms but many can still only cope with 4 Ohms. Please check you amplifier specification to find out it's minimum load.
Only connect the same kind of loudspeaker to the same amplifier channel. This will ensure proper phase response of the system and allow the correct processing.
This calculator uses the formulas Published by the BBC amongst others.