IMHO, you can't do what you want to do with just a cable. You would need a speaker level to line level convertor.
Something like this:
http://www.amazon.com/PAC-SNI35-Adjustable-2-Channel-Converter/dp/B001EAWS3W/ref=sr_1_1?s=electronics&ie=UTF8&qid=1407020301&sr=1-1&keywords=line+output+converters
There are a lot of different ones out there from very inexpensive to not so much.
I have never tried this, so I have no idea how it would sound.
Something like this:
http://www.amazon.com/PAC-SNI35-Adjustable-2-Channel-Converter/dp/B001EAWS3W/ref=sr_1_1?s=electronics&ie=UTF8&qid=1407020301&sr=1-1&keywords=line+output+converters
There are a lot of different ones out there from very inexpensive to not so much.
I have never tried this, so I have no idea how it would sound.