Speaker cable to stereo mini plug adapter?

Hello,

I'm wondering if there is any such thing as a regular copper speaker cable to stereo mini plug adapter.
The thing is, I have speakers built into the wall and ceiling with speaker cables (4 strands of copper, I don't know what gauge)coming out from the wall. I would like to connect this cable to my receiver or an iPod so I can listen to music from the speakers in the wall.

It can be something like speakers cables -> RCA female -> stereo mini plug. The connection does not need to be direct.

Any help, suggestions will be greatly appreciated.

Thank you for your reply.
Yes, that will work, but the problem is, the wall where the speaker cables are hanging out from, is about 15ft away from the receiver and where my TV is. So I wanted to just use the in-wall speakers for the occasional iPod music listening. Also, the new speakers/receiver system I'm thinking about purchasing does not have any speaker cable interface (only RCA)...
If there is nothing I can do to easily convert the speaker cable to mini plug, how would I go about extending the speaker cable close enough to my current receiver?
I'm sort of stuck in a place where all options seem like a second choice.
Thanks again for your help.

Thank you.
I was hoping there will be a small powered device that will serve as an adapter or something of the equivalent, but it sounds like there is nothing i can do except extend the speaker cables and find a receiver with the speaker holes (or clips or whatever it is called).
Do I understand correctly that I would need a crimp-on butt connector to extend the current speaker cables? Would this in any way compromise the sound quality? Not like I have any choice considering the cables are already inside the wall, but I just want to make sure.
Thank you.

Great, thank you jimbowne and rexter!
I'll try my luck with extending the speaker cables.