Loudspeaker Cable - Naim Nac A5 vs Kimber 4TC (single vs biwire)

Hi All cable fans, i have a nice Primare Amp and nice Elac 507 Speaker. I just used my old Nac A5 cable as I had this at home. Sound is great. Anyhow I was reading that this cable might have slightly disadvantages on the heights. 
So I attached a new Kimber 4TC as biwire cable just for the mid/hi-pass. The Nac A5 is now directly connected to the low pass. I clearly took out the interconnector between the hi/mid & low-pass. 
I was expecting any improvement of the mid/hi‘s,
but the result is absolutely nothing 🤦‍♂️. No change of the sound, no improvements :(. Thats a pitty and wast of money. Did I learn that biwire is wast?!?!

ps: I hope the cable will open over time if this magic exist..
Out of curiosity did you try switching the two cables, Nac A5 to mids and highs and Kimber 4TC to bass? Did you hear a difference or did they sound the same?
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I tried once the 8TC for the bass, and i have the same result with this 4TC AC = bass is not good! The bass become less precise, less punchy and more booming. Same effect like with a too small amp. 
Okay then I will put only the 4TC on the speaker on Friday, where I go 1 week ago. I will let the musik run 1 Week :-). I hope its not important to make it very loud as i have neighbors. 
The music does not need to be loud, the important thing is a signal running through the cables.