Inexpensive Tri-Wire Cables

Analysis plus has cables in different guages that work great together. If you contact them through their web page analysis-plus.com they will custom factory-terminate whatever you need.

You could even schuffle with different single-wire factory terminated cables or mixing a single-wire with bi-wire for a "larger room of experiments" but it's truly pain to connect two or three spades onto one binding post(bananas cannot be connected a few onto one binding post).
I think it makes a sence to have a different gauge and grade for upper binding post.

Alon makes a tri wire arrangement for their speakers which is not very expensive.