Reply to Cables, how much are they important in the sound?

Hi all!

Been believeing about this all day, and I can't get a proper answer. How much important is a good RCA cable? will the sound change? i.e. more bright in the middle tones, a more tasteful low-range, etc.. The same for speakers cables (I mean speakon and XLR for active boxes..)

What do you use in your setup? Have you tried any other cable?

Regards!