I use either an RCA cable or mini cable with all my radios and sound systems on aux. If they don't have Ipod/MP3 option (and most don't). The cables are $8- 12 and for the harder ones to get to (like my big Yamaha system with Klipsch speakers) I leave cables hooked. I admit most of the time I use the Touch but sometimes the Ipad. I listen to Pandora, Rhapsody, Public Radio app, my own music., whatever. This way I can move the music to where I am. This summer I used a cable with a powered outdoor speaker at the pool. Either the Ipad or Touch or Iphone works for a portable music system. Oh, my Sony system can use the USB cable.
I love the idea of using found/cheap speakers but I'm not good with DIY.