Kind of a tough one. You’re right in the middle of needing more speakers because of the size of the room but not having the ability to drive more than a 4 ohm load. The amp you have should be able to drive two pairs of 8 ohms speakers but you may not get enough coverage for the size of the room.
Hi! My choir room is 30 x 40. I`m looking at putting ceiling speakers in for 2 reasons. 1) even sound throughout the room and 2) appearance. I have an Alesis GigaMix6FX which is 300 Watts/4 ohms x2 (600 Watts total). Can you recommend in-ceiling speakers that would work with this powered mixer and how many speakers would you suggest? Thanks!