Why do you think Bi-Wiring improves the sound ?

I go by the fact that if some speakers have the capability, then why not use it in that manner (biwired), can’t hurt...the speakers with just one set of terminals, well then, I have nothing to fret about as there is the one option. I can’t say that I’ve heard an astounding difference, if any, in sound quality, but I’ll use the speaker in that manner if the design allows. Plus I’d rather biwire where applicable rather than use the crappy metal jumpers provided any how.

Not that it would directly pertain to your situation, but simply improving the jumper situation can have a noticeable improvement...or change, rather. I say this for perspective, as I would not conceive of going to the trouble of changing a crossover to add extra posts. Just improving the crossover with better wire/connections, caps, resistors alone should be more than sufficient. I’m sure I’ll receive some flac for suggesting this, but would it not seem that a biwire configuration would be taking into account cabinet and driver design? Some of the very best speakers out there only have one set of posts. But my current speakers (totem arros) have two sets, and when I simply changed out those factory brass honkers with silver plated audioquest wires...wow, a real improvement (to my ears, anyway). So maybe just some improvements to the existing crossover, unless those parts are already pretty fancy to begin with? 

It doesn't make a difference.  And the whole diagonal wiring thing is another nonsensical myth.  I implore you to try it for yourselves, but make sure no alcohol is consumed between the time you start the wiring experiment and the time you sit down to listen.  

Richard Vandersteen insists his speakers are bi-wired per his design, so I bi-wire mine, and have never used jumpers on my Vandy’s. Not sure what the big deal is. I’m certainly not going win an argument on the subject with Richard, and have never seen anyone who has when confronted with the subject.

Now, if your speakers only have one set of binding posts, I see no good reason to add them if that is how they were designed.

The only benefit of bi‐wiring is the increased speaker wire gauge equivalent you get running two sets of wires. Running a twin set of wire is equivalent to increasing the speaker wire guage by 3. For example, running two 14 guage wires is equivalent to running a single 11 guage wire. I have tried both routes and I would say If the cost is minimal, there is no harm in running a bi‐wire setup. I wouldn't go to the trouble of adding dual binding posts to a set of speakers though to accomplish this.