Do speaker cables really matter?

I'd second Rockvirgo's comment; have you tried going back to the Kimbers for another listen, just to compare? Renewing the physical contact at the amp and speaker ends can make a noticeable impact on sound, often attributed wrongly to the new cable.
I'm not saying cables don't make a difference (I switched from heavy copper to silver speaker cables and noticed a very small change in frequency response), but they may not be responsible for the change you hear.

For years I was skeptical but they indeed make a lasting and audible difference; as someone said above, unfortunately.

I've found that, in comparison to Tara, Synergistic and van den Hul, Harmonic Technology ICs and speaker cables provide me with the timbre and frequency balance that suits my tastes from Joni to Zep to Miles to Beethoven and everything in between and around.

Yes, they matter. I think, the most important cables are the ones for the speakers and from Tonearm to preamp.

Thomas, you have a beautiful system, and I'm sure it sounds wonderful as well! Have you worked with aftermarket power cords? If not, you truly owe it to yourself. I have found that power cables seem to make nearly as much difference in my system as speaker cables. I hear very clear, significant changes to the system instantly when I use different power cords. If it were so subtle that it was negligible I would not recommend it.

If you are well aware of all this, excellent! I was not able to determine from your post whether you had worked with specialty power cords. I did a quick check of your system but did not see any listed. :)

Shadorne - I read the article. It is strange that he describes cable as DC component while impedance of typical cable is few times higher than resistance at few kHz. I also disagree a little with his skin effect assestment (no skin effect in audio). Skin depth is affecting audio frequencies (a little).

The wire where AC and DC resistance is the same (skin depth S is equal radius) for copper and 20kHz is Gauge 18 (40 mils Dia).

Lets take 10 feet of gauge 14 (very popular Audioquest type 4). DC resistance (counting length both ways) is 20 feet x 2.525 mohm/ft = 50.5 mohm but AC impedance at 20kHz is equal Rac=Rdc*k*sqrt(f) (where k is a gauge factor (k=17.6 for gauge 14) and f is frequency in MHz) and is equal 126 mohm.

Difference between 50.5 mohm and 126 mohm might seem not important (less than 0.1dB divider) but it limits DF at 20kHz to 64. Stranding wires with isolation between strands increases effective surface but strands being in sum of magnetic fields are still subjetc to skin effect unless they're wooven on the outside of the hollow core (hyperlitz).

Don't get me wrong - I am not trying to prove anything here. I'm just trying to make some sense of it and to understand why cable manufacturers come to similar design solutions (like hyperlitz). My Acoustic Zen Satori has some kind of hyperlitz (they don't call it that) - wires woven on hollow tubes. I do not believe in the cable companies conspiracy to sell snake oil. We can hear the difference - explaining it is hard to do.