Night and day speaker connection

It's very possible that you are hitting that threshold where awg makes a difference.  If you "bi-wire" a standard set of speaker cable (such as Audioquest, which is only 13awg to begin with), you are essentially splitting up the amount of conductors.  On a 13awg Audioquest cable, your "bass" bi-wire is only going to be 15-1/2 awg, and treble is 16-1/2 awg.

Doing a bi-wire on a much larger cable would likely work much better, like if the main cable was 9 or 10 awg.

There is a simple explanation for this. You have effectively doubled the gauge to all the drivers with speaker cable. Imo the change is not primarily due to moving to use of a jumper, but by supplying the entire works with double the speaker cable. 

When you split the bi-wire cables, you had half the gauge going to each set of posts. Now, you have doubled the gauge to the speaker via speaker cable. That is a huge difference in performance and is imo the greatest reason for the improvement. 

I always do that when I use jumpers, that is, use a pair of speaker cables to the preferred set of posts for the input. You can reverse it and remove one set of cables from the posts, and you will have a diminishment of the performance globally. 

And now, the coup de grace, are you ready? There is a superior option better than what you just did. It would involve four pair of speaker cables, yes, double bi-wired. It is another step above doubling a set of cables with jumpers. Most would not do this because of cost/availability of cables. However, if I am not mistaken, you have plenty of cables. ;) 

You are correct; the quality of the jumpers is very important. :)

Thanks guys, you confirm that I am not only dreaming... 

This is whats called "shotgunning"?