speaker cable that would work under a rug

@tksteingraber +1 if you want to go premium. Check the Cable Company.

I have runs of about 14 feet of Goertz MI 1 flat copper under family room large area rug. Works great.

Happy Listening!

Any good heavy quality cable. I bought a roll of it 5 years ago for an under the rug run in my living room for my rear surround speakers mounted on the wall ing a large area throw rug over tile and it's worked great.

Can you get in the attic to run them?

That's what I did, through the attic and down inside the walls. Very Clean!

There is a company called "the cable Company. https://www.thecableco.com/

They have an excellent selection of all sorts of cables. I have had good luck with the Goertz cables. They are specifically designed as being flat, as in wafer thin flat. I believe if I remember correctly you buy by the foot. Good luck. 

@mcanaday 

I would never run cable under a rug. If you have continuous wall down one side of the room (no doors), I would get a heavy gauge pair of speaker cables and run them from your amp along that wall to your speakers. Any excess cable can be loosely coiled behind the first speaker in the run. I have thirty feet or nine meters of Kimber Kable 12TC in my room. Though the capacitance is rather high for each leg the total run at around 4400pf, using any kind of ribbon cable is significantly going to exceed that. There are some amplifiers of somewhat questionable design that would be adversely affected by that, probably an OTL and some direct coupled solid state but that is rare these days. Amps with output or auto transformers are especially immune because they protect the output devices from the effects of the load to a great extent.