Possibly dumb question: can I use two cable runs for each channel, not bi-wired?

Thanks a lot for your helpful response, Al; it's much appreciated! 

You’re welcome! One more point: Be very careful not to mix up + and -. Specifically, when two speaker cables are connected in parallel if + and - are interchanged at one end (and only one end) of one of the two cables (but not both cables), the result will be a direct short across the the amplifier’s + and - output terminals. Which of course would definitely not be healthy for the amp.

Regards,
-- Al

Yikes!  I will be extra careful! 

You will be fine. As you noted you are producing what cable makers call shotgun cables. They double the wire and either combine them in two terminations or four terminations. I would just mark the end of each wire with a color tape to make sure you don't short anything out
Alan

I use double-cables two ways: 

a) For amps that I've owned having two sets of speaker outputs (Adcom and Krell) I have bi-wired by using both of these outputs and two sets of cables to bi-wirable speakers, like my B&W805D. 

b) For speakers that are NOT bi-wirable (my Thiel CS3.7) I run two sets of speaker cables and double them up on the speaker terminals. I'm doing this with two sets of Nordost Heimdall cables that I made from a single, really long run. I found that this added a little something to the sound. I think the additional cable mass makes a difference. Perhaps this is in line with Nordost's move toward more cable mass in their newer models.