As to the question, how many watts you need depends on the efficiency of the speakers. The "150 watts" part means don't expect to feed one of these speakers more than that.
Efficiency is shown as 89 dB, one watt at one meter. What's not obvious is that most indoor speakers run at about one watt or less for most music, especially background music. Outdoor speakers' sounds are not contained in a room, so more power is needed; outdoors there is usually more noise, so yet more power is needed.
I'd want to be able to feed at least sixty watts to each speaker. It's been said that six to ten dB louder seems like twice as loud to the ear; six dB more than sixty watts is 240 watts, and ten dB more than sixty watts is 600 watts.
Do you have ANY amp at all? Try one out!
The average AVR is optimized for surround sound, and often has a second zone that, in many people's opinions, should not be used to run more than two pairs of speakers.
I feel like I'm rambling, and it's late. If this inspires any questions, ask away -- it'll help focus the answers.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
