Bi-Wire with two pairs of speaker cables

Bollocks! When will audiophiles realize that changes they make to their system is specific to their system only?!?!?!

The reason for BiWiring is to stop woofer current from modulating tweeter current.

It is totally permissible to use two different cables.

Each and every combination will have various effects.
Jumping one of the legs at the speaker will sound different on every speaker.
Separating the cables will change the inductance and thus the sound. I like mine interwoven.
There is no need to have dual amp outputs, two spades on one terminal or two leads into one spaded is fine. Adding a second terminal adds additional LCR which may or may not alter the sound depending on the components chosen.

In ALL cases, audibility is program, system and listener dependent.

Ignore fan-boy recommendations, experiment and keep what sounds best to you.

Please see http://ielogical.com/Audio/CableSnakeOil.php/#BiWire for a BiWire analysis.

Bi wiring a tube amp is very effective when you have 0 - 4 - 8 - 16 ohm connections. Use the "4" as "common" and the "0" for woofer, and the "16" for the tweeter. Polarity of the tweeter may have to be reversed. Easy enough.
Now the thinner (usually) 16 ohm wire inside the transformer only carries the tweeter current. Thinner wire has better skin effect properties for higher frequencies too.
The voltage on 0-4 and 4-16 pairs are the same but phase is opposite with 4 as neutral. 8 has lower voltage, which can be OK is the tweeter is "hot" and you want to lower it.
Try it. Nothing bad will happen.

I’m a big proponent of biwiring.  I use homemade silver braid on my lows, limber monocle for my highs and I love it. Cleaner tighter bass, colorful mids, crystalline highs!

FYI: I've used the method with good success that williewonka suggested above. Give it a try...

@thyname

I do not dual wire my speakers ...I tri-wire them, and like others who have posted I use identical cables when tri-wiring. No problems here. My speakers are vintage from the early 1970s - a pair of Pioneer CS-A700's - but the cable is new. Pure copper cable. USA Made. Make certain you label your cable runs. I suggest labels at both ends and in the middle. To my ears tri-wiring is wonderful.
But then, my ears are vintage - just like my rig.
Happy listening.