Newbie here, and do-it-yourselfer... Our house is pre-wired for a home audio system. I have 10 zones (1 to 4 speakers in each zone) and 2 of those zones are outside. I'm pretty sure the speakers are 8 ohms but I need to pull one out and double-check. Each room has a simple volume control. I just picked up a speaker selector (Niles MSA-10A). Now I need to find a receiver capable of powering the system. We only want one source (plan to plug PC into receiver and use iTunes so we can control it remotely via iPhones). We're fine with listening to the same thing throughout all zones; no need for different music in different zones.
So what are the minimum power specs for a receiver that won't under-power the system but also won't bust my wallet?
How many watts do I need?
Is there anything else I should consider besides watts, given that I have a speaker selector with impedence matching?
Niles claims the switch box has autoformers which allow simultaneous multiple speaker operation without loading down the amplifier. This should provide sufficient protection for the amplifier, so, in theory, you could buy whichever receiver/amplifier you prefer.
The sensitivity spec and impedance of the speakers is more important than the number of watts you have. Doubling watts gains you very little in actual volume, the difference between 75 and 150 watts is virtually not recognizable under normal music conditions. The higher wattage does provide protection against clippping the amplifier on peaks so IMO the best advice would be to do one of two things; 1) return the Niles and use the money towards a multichannel amplifier that dedicates a stereo pair of channels to each zone, in your case it would appear you would want a 10 channel stereo amplifier (grouping two channels in one "channel"), or, 2) buy as many watts as you can afford in a receiver/amplifier. The quality of the watts is far more important than the quantity of watts so buy something that advertises it is happy at less than a six Ohm load and you should be in the ball park.
Outdoor speakers do eat up quite a bit of wattage since they are typically not working with the reflecting surfaces found within a room. No matter how many watts you buy there never seems to be enough for outdoor speakers to get much beyond comfortable background levels. Placing the speakers close to the seating positions makes more difference here than watts. If this isn't possible in your situation, just make sure you're not clipping the amplifier trying to get volume to the speakers at the far end of the pool.