Can I "double-wire" speakers?

You sure can. Bi-amping is a common practice that will really let those speakers sing. Let use know what you think.

STOP!!! Let's clarify this first. You can only do this if you REMOVE the jumpers on the speakers and have one unit driving the low frequency posts and the other driving the high frequency posts. Do NOT hook up each unit to the same posts. This would be very bad.

I would remove the jumpers on the speakers and have the Onkyo hooked up to the low (bass) posts and the Sophia hooked up to the high (tweeter) posts.

I doubt that both amplication sources will have the same gain.

Gotcha. I'll remove the jumpers between the two sets of binding posts and see what happens. I haven't received the Sophia yet, but I suspect I won't get the same bass response as I do from the Onkyo with its Velodyne sub.

Then again, this might all be a moot point if the Sophia performs as well as advertised.

Thank you for all your advice.

If you are trying to use the two amps as two seperate systems driving the same speakers,no. The top connections are connected to the mid/high x-over and the lower ones to the low x-over.