Bill O: Sounds like your original cables were pretty lossy and I'm guessing add some distortion as well.

For speaker wire I think getting the gage right is the most important thing and the other factors not so much. I just strip the wires and and tighten the nuts. Here's the resistance in ohms/foot for some of the various gage wires (copper):

10 .00118
12 .00187
14 .00297
16 .00473
18 .00751
20 .0119
22 .0190
24 .0302

As an example, running 18 AWG wire 20 feet will give a resistance of roughly 0.15 ohms. If your speakers are nominally 4 ohm then roughly 7% of your power is lost in the wiring. Go with 12 AWG and the loss gets down to less than 2%