That receiver you have is just fine. I would opt for less speakers and better quality if you are trying to save money rather than more speakers in the cheapest possible junk. That Colby stuff will probably drive all of your customers (and any mice) out of your shop! If you are trying to spread the sound throughout the shop with fewer speakers then put them sideways or bounce the sound off the ceiling or wall etc. Keep them up high on the walls if possible.

RR6