Well, there you go, ratatoskK. I didn’t know about that product, but it seems to do what you want, for only about $110.
However, it’s a “Wireless **Rear **Speaker kit” and is intended for use in a home theater system where it may be hard to get wires to the rear speakers. It may work for your purposes, but it’s not really intended for main speakers.
For one thing, the power output is only 25 watts to 4-ohm speakers, which is pretty low. And the harmonic distortion is “no more than 10%,” which is horrible. The other big problem I see is that the volume control at the receiving end is not really user-adjustable. It’s on the back panel, and is intended to be set once and left alone. The output is actually controlled by the sending audio source.
I would guess that if all you want is background music at the remote location, it might work well. But if you expect to crank it up, I doubt you’d be happy with that solution. Maybe caveman can tell us more about how he uses it, and the volume levels and sound quality he gets.
There are similar systems (much less expensive than the nice system Tim R. Mortiss linked to) that transmit a line level signal which you would then put through a receiver or amp of some kind at the remote location.
For instance, the Terk LeapFrog wirelessly transmits audio, video, and IR remote signals. It looks funny, and I have never owned one, so I can’t recommend it from my personal experience. (I have the predecessor unit that uses telephone wires, and it’s performed perfectly for more than a decade.) But it’s also relatively cheap, so it won’t cost much to try it out.
With the LeapFrog, or something like it, and a relatively inexpensive receiver (e.g $100-200), you could get much better nominal performance than with the Rocketfish, and have additional features, like volume and tone controls, the ability to select other sources, like a CD player or FM tuner (probably built-in), and so on.
Or if you have an independent source at the sending end, like a TV or something, you could use your Sherwood at the receiving end.
Again, we need more information on your situation, existing hardware, and goals in order to advise you more intelligently.