johnw, the two speaker brands mentioned would surely do a good job, the QSC's have good reputation. Self powered speakers are probably what you want to use for a backyard type projector set up as that eliminates the need for outboard amps.
I used to work for a company which designed home movie theaters back in the late 1990's and have two opinions for you which may or may not influence what you do.
1] the 1/8 inch output certainly reduces the quality of signal you will wind up with- I took a quick google trip around and noticed many projectors have no sound outputs, although I did see some Epson's which do. I also found that the Apple TV device puts out several types of audio including Dolby 5.1 and 7.1. If you wish to go with a center channel you may need an AV type pre-amp to interface from the projector/Apple TV device out to the amplified speakers. No brand rec's from me, others may have some.
2] I understand you want to keep it simple, but from my experience the center channel when playing movies is very important to the experience. Most movies are not mixed in 2 channel stereo and they have a dedicated center (mono) channel for the dialogue. The HDMI output from the Apple TV should contain center channel audio. I have not been in the field since the invention of Network streaming devices such as Apple TV and such, and probably am not the ideal person to recommend brands, but I am thinking you'll have a much better experience by finding an AV pre-amp which will output three channels and use three of whatever brand self powered speakers you choose.
I will add that my interest in this topic had me reading a bit about backyard theater set ups. You can surely do what you originally requested with just a two speaker set up, self powered ones become the obvious choice.
I found these two links which may help with ideas (this guy used Sony speakers): http://www.hightechdad.com/2009/09/08/how-to-set-up-an-inexpensive-outdoor-home-theater/
From this link: http://www.cnet.com/news/can-you-build-a-backyard-theater-on-the-cheap/
I found this paragraph which likes the aforementioned Behringer speakers:
Now for the really tricky part. For movie audio, the aforementioned Open Air Cinema kit combined a Rolls MX122 MiniMix Pro sound mixer (available separately online for about $100) with a pair of Behringer Eurolive B208D speakers (about $180 apiece). If you've got room in the budget, I can't recommend this combo highly enough; the sound quality was phenomenal (and loud).http://www.amazon.com/Behringer-EUROLIVE-B208D-220-Watt-Compression/dp/B002C4QWZO/http://www.amazon.com/Rolls-MX122-MiniMix-Channel-Mixer/dp/B00102XVN0