Stereo Mini to 1/4
Details of connections: MP3 player to Bose System
Plug this into your MP3 Player (headphone or line out jack) (black end to MP3 Player)
and attach coloured ends to this:
Male (pointy) end then plugs into
Channel 1 or 2 (allows control of tone and relative volume from R1 Remote)
-= or =-
Channel 3 or 4 (control from music source)
You could get two RCA to 1/4" adapters, but then you would have to use both channels 3 & 4. Since the L1 is mono, there is no particular reason to use two channels.
Click the images to see the ordering information if you want to get them from Radio Shack.
(disclosure: I have nothing to do with Radio Shack but they have decent pictures).