what cable should I buy for my system?

I agree with @jond Try a good preamp. Source to amp is typically forward and doesn’t excel in layering and soundstage. 

There are Cable Suppliers that that offer a no obligation to purchase home trial for 30 Days. Using such a Cable Suppliers offer, will enable the individual to expand on their experiences.

When expansive experiences are able to be had on the Home Audio System, or an Audi System that is very familiar to oneself,  the benefits of the learning to be attained are much more that when being sought on a unfamiliar system.

Talking about and trying to decipher descriptions offered by others is no substitute for a Direct - Sat in Front Of Experience.

As for a Wire Type used for the Cables Signal Path. PC Triple C or D.U.C.C Wire Types are ones I recommend today.      

Thank you for your help.

Unfortunately, there are things I can only describe with a translation. I apologize for that.
So my biggest concern is that the sound doesn't have an ideal space. Fine details are also missing.
At the moment I have a Fidelity achat pre-amplifier asymmetrically.
I currently use plain transparent cables.

Has anyone tried michi's own preamplifier with the michi m8 and B&w d3 series? what will happen with p5 or without p5?

Thanks

…….go listen, talk to friends , read the posts here which means YOU might have put some time into this , make some mistakes snd then YOU tell us 

I bet if you did a blind listening test of cable A versus cable B between preamp and amp you wouldn’t be able to tell them apart. The brain is easily fooled when sight is involved.