Agaric (well, benjamin) wants wireless headphone out to music port line in transmission

Logitech has one

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2074986&CatId=197

This seems to be it but it's ridiculously expensive:

Creative X-Fi External Wireless Xmod
http://www.novatech.co.uk/novatech/specpage.html?CRE-XMODW
Creative's Xmod Wireless streams music in Xtreme Fidelity from your PC, notebook or MP3 player around the home. Simply connect it to the USB port of your computer or the headphone socket of your MP3 player, place the X-Fi Wireless Receiver in any room, connect speakers or headphones - and you're ready to enjoy your music, wire-free!
£143.75 inc vat

An article with no useful links had this to say:

a small transmitter is connected to the Line Out port of the sound card, and a matching receiver is connected to the Audio Line In port of the receiver. Music from the computer is silently broadcast via radio waves from the transmitter to the receiver. The receiver interprets the radio signals and translates them back into an audible signal to play through the speakers of the entertainment center.

Wireless stereo transmitters vary in design and pricing and a few models are expressly designed for iTunes music. Others include composite video ports to send not just audio, but video signals between the computer and entertainment center. Cables might be included or sold separately. For more information check your local electronics stores or your favorite online retailers.

Jensen's new Matrix Wireless Internet Audio Transmitter is
http://www.smarttvandsound.com/article/8216/

Resolution