You may not need any "bridge," at least for the Mac, and if your goal is to play audio FROM the Mac TO the player.
AirPlay is Apple's method of streaming audio. As in sending to another device. UPnP devices can't usually receive such (some like Raspberrry Pi running XMBC can, and there are others). But many can access audio (or other media) FROM the Mac; i.e. you are using the player to get audio from a Mac rather than a Mac to send audio to the player.
Consider Playback, a software solution. It makes audio, video and other stuff accessible to UPnP devices from a Mac. I use it with a PS3, for example. Check Yazsoft; they have a list of compatible devices. You might be able to do photos too depending, again, on the capabilities of the player. The key here is that the player must have a way of accessing stuff on a network. Anything running XBMC can, for example.
If, on the other hand, you need to use the iPad or Mac to send or stream, you probably can't do it via AirPlay. AirPlay only works with certain receiving devices, as Macman45 noted. And those would essentially bypass or substitute for your player and output to your speaker or amplifier system. So would an Airport Express, or an old iPhone or Touch if you run Airfoil and Air Speakers.
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You may not need any "bridge," at least for the Mac, and if your goal is to play audio FROM the Mac TO the player.
AirPlay is Apple's method of streaming audio. As in sending to another device. UPnP devices can't usually receive such (some like Raspberrry Pi running XMBC can, and there are others). But many can access audio (or other media) FROM the Mac; i.e. you are using the player to get audio from a Mac rather than a Mac to send audio to the player.
Consider Playback, a software solution. It makes audio, video and other stuff accessible to UPnP devices from a Mac. I use it with a PS3, for example. Check Yazsoft; they have a list of compatible devices. You might be able to do photos too depending, again, on the capabilities of the player. The key here is that the player must have a way of accessing stuff on a network. Anything running XBMC can, for example.
If, on the other hand, you need to use the iPad or Mac to send or stream, you probably can't do it via AirPlay. AirPlay only works with certain receiving devices, as Macman45 noted. And those would essentially bypass or substitute for your player and output to your speaker or amplifier system. So would an Airport Express, or an old iPhone or Touch if you run Airfoil and Air Speakers.