Below is info and a link to what appears to be a fix that comes from the car audio industry. I've ordered one and am going to test it. Not bad for a $20 fix if it works!
TWO CHANNEL HIGH QUALITY LINE DRIVE ADAPTER
I can't post the link, but google David Navone and you'll find it.
There are many others out there, some more expensive than others. Noise could be an issue, but we'll see! If this one doesn't work, I'll find one that does!! Will post results after receiving the adapter.
Am also using a single Sonos Zone Player (LightSpeaker transmitter RCA'd to the RCA output on the Sonos) with the Iphone app to control the music from from Iphone.
Apple Remote App can be used on a wifi touch or Iphone as well to control your itunes library on your computer, if the computer is one of the sources. You can view cover art, change songs, mute, volume up/down all from your IPhone or touch!