can one play iTunes music on multiple Apple TVs simultaneously?

Yes. From, iTunes play the music and select the airplay icon [bottom right] and select the AppleTVs to play the music. I use it for one AppleTV and two Airport Express with atttached speakers. Fills the house with music. Great for parties.

If you have an iPhone, iPod Touch or iPad with the Remote app, you can control your iTunes music and the selected airplay devices. Adjusting volume and selecting music or pausing when a speach is being made at your party.

This sounds interesting. Here is my current situation. I have a mac mini downstairs connected to my TV via my stereo receiver. I have a LG bluray networked soundbar connected to my TV on the middle floor (also has an xbox connected to the LG), its also is a stereo receiver. How can i use airplay to play music on multiple floors? I know the mini has airplay, and i have an iphone and ipad. Im thinking i would need an apple TV connected to my middle floor soundbar? Will i be able to send music downstairs to my mac mini using airplay?

the only appletv which can access other airplay devices is the appletv1g the newer ones can only be used as speakers not use others themselevles

Found this article today:

http://howto.cnet.com/8301-11310_39-20049405-285/apple-airplay-10-things-you-nee d-to-know/

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• Using your iOS handheld as a music source has limitations.When you stream music stored locally on your iPhone, iPad, or iPod Touch, you can only stream it to one device (such as a speaker or Apple TV) at a time. You connect to that device using an AirPlay-compatible app and it becomes a monogamous streaming relationship.
• To stream to multiple devices, you have to use your computer-based iTunes music collection as the audio source.For whatever reason, running iTunes on a Mac or Windows PC provides more flexibility for AirPlay. Using iTunes on your computer, you can stream music to multiple AirPlay receivers or speakers throughout your network (say, an Apple TV in the living room and aZeppelin Air in the bedroom), and control their volume levels independently as well.

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What I'm trying to figure out is if I can send music from my imac to my apple tv and to either my iphone or my ipad at the same time. The imac will only let me select the apple tv or itself in the airplay drop-down. I can send music to the apple tv from any of these devices but not to them from the imac or the apple tv. I would love to have the same music playing throughout my apartment at the same time and this would allow me to do it since I have speakers set up with a mini-jack plug for the iphone or ipad in the kitchen.

No you can't. You can only stream from mac to apple tv or an airplay enabled speaker, not to an iOS device. You can stream from your iOS device to Apple TV or airplay enabled speaker, or use the Remote app to play music from itunes on your mac and listen to it on multiple airplay speakers (same goes with remote to apple TV). But you cannot go from Mac to iOS device, its only one way from device to Apple TV. You can't even go from iOS device to Mac computer, has to be Apple TV, or use the Remote app to access itunes on your computer.