Here's my situation: I have a Klipsch Promedia 2.1 system and the left channel died. The left speaker works fine when plugged in the right speaker output on the sub. Right now I have both speaker wires in the right speaker output in the sub so I get the right channel on the L and R speakers. Is it possible to play both the left and right channels on the iMac through the right channel so I at least hear everything from both channels?
Open System Preferences > Sound > Output. There's a slider that allows you to change the balance between the left and right channels. Sliding it all the way to the right will play all the sound from the system through the right channel (essentially mono instead of stereo).
Buy a mono 3.5mm audio cable, plug it in, you will have both output channels hard-mixed and played on both speakers.
If the cable on your speaker is non-removable, simply buy a 3 inch male-to-female one.
And if you can not find a cable like this, go to a shop that sells audio cables for guitar players and ask one to be made for you. You will hardly pay more than 10 bucks on such a thing.
Analog solution to a digital problem, YAY!