Txp1,
Interesting to hear no ground loop hum for you on your XM. That is good for you, and perhaps I will have to try it again.
As for speaker cables that are flat, I personally have no experience with such a cable. After reading you need a 25 ft. run I too would hesitate to change! I choke at the prices I pay for 6 ft. runs!
Since you will most likely not find a company with a 25 ft. "loaner" to audition, you may want to call someone like The Cable Company and explain your equipment and your current cabling. They will then ask where you would like to make an improvement in your sonic presentation, and in my experience they are normally very good in making a precise recommendation. They will usually offer a few recommendations in various price ranges as well as which may work best in what areas...

