Why do you think Bi-Wiring improves the sound ?

I didn't see any benefit from bi-wiring.  Active bi-amping, on the other hand, with my Magnepans (built to biamp) was a huge jump in sound quality.  Literally, veil lifted off.  

No,  but it was really obvious, no need, not at all subtle.  I'm not a tweaker or believer in fancy cables, gold plated power connectors, any of that crap.  But bi-amping is a substantially different equipment configuration that is naturally going to sound very different.  Part of it is I think the 30-year old crossovers in my Maggies probably need refreshing, and so using an active crossover is a better bet.