Does such a product exist ??

A wireless router and a Squeezebox Touch is the perfect solution. The wireless router plugs into your computer and the Touch plugs into your DAC.

Sonos does this also.

Both Sonos and Squeezebox are great options for what you are looking to do.

*****Sonos dealer*****

I was at my dealer recently and he showed me a Sonos system. There are similar products as well, I can't comment on which is best. But the system was really cool, he had music in several rooms and remote controlled from an iPhone (he had an iPhone, I suppose other phones do it to).

The Airport Express or an Apple TV device do just what you're describing, as long as you're using iTunes to manage your music files on either a PC or a Mac. You can use up to three Airport Express devices at once. I've got one in my living room and one in my basement taking a wireless signal from the Mac in my office.

The port on the Airport Express or the Apple TV outputs a digital signal through a mini-Toslink connection, which goes into a Toslink input on your DAC, assuming you have one. An analog signal is available from the same port by using a mini-stereo plug but the quality won't be as good as using the digital signal through a decent DAC.

The retail is $99 for either box and the Airport Express is usually available refurbished from the Apple Store for $69. If you don't need the wireless router functionality of the Airport Express the Apple TV is probably a better deal since it does all kinds of other cool stuff, as well.