Ok,

I have two audio sources(XM and Sirius satellite radio) that I want to connect to my home stereo, both use a 3.5mm minijack for output. I have one spare RCA input left one the receiver (R + L, so red and white). As it is now I have to unplug one source and plug the cable into the other to switch. Both are never in use at the same time so I don't need a switch box although that would work I guess. What I'm looking for is a cable that has two minijack male ends and one (L+R) RCA male plug on the other end. Does such a cable exist? I've googled around but haven't come up with anything. Thanks!

Cables such as what you describe probably exist but you're not supposed to use them to do what you want. The impedence and therefore the signal quality will go to hell because you're not supposed to have two outputs wired together like that. To do it properly you need a mixer or a switch.

OK, thanks! That's why I couldn't find anything. I'll start looking for other solutions.

Well to do it properly you need either a switch box OR a mixer.

Switch boxes can be automatic though. I'm fairly certain you can get a switch box which automatically selects which unit is outputting a signal. One of the inputs would have priority so it would switch to that if both units were on.

Can't seem to find anything in a quick Google, but I know there are at least AV versions of the same thing.

The circuit you need is incredibly simple and can be easily made if you've got basic soldering skills. If you want to save some time then just buy a stereo 3.5mm male to male cable and a RCA male cable then chop them up.