Speaker cable: 4 or 2 per speaker?

Yes, I would try it if I were you.

I assume your speakers are NOT the bi-wire variety. What you can do is use an entire separate run of cable for each terminal on your amp and speakers. In other words, use one whole cable from the +(red) of the amp to the +(red) of the speaker; then -(black) to -(black), etc, etc. (A separate whole cable per speaker and amp terminal equals 4 pieces.)

If you have bi-wireable speakers and never have done it; then remove the jumpers on the speakers, and use two cables from the amplifier per channel to each pair of speaker terminals.

I do have bi-wireable speakers. Can I expect an improved sound using 2 wires per speaker? Should I sell the Slate and get something else? What do you know about Virtual Dynamics speaker cables? I have their IC and PCs and love them.

I actually used a double run of AQ Slate for biwire for a few years. Worked very well. I had them professionally terminated, so the two separate cables were combined at the amplifier end, since my amp had only one set of speaker terminals. If you're using bare wire, you can just combine them at the amp end, unless your amp has bi-wire (two pairs) terminals also.