Hi, Audioangel,
I would say they don't have a sound. They just sound like music. They make your system sound like you might have always thought it should sound. At least that's what they do for my system. The more my system has improved, the Synergistics have gone along, right in stride, showing each and every improvement, large or small. For me, I am content to just ride on them, I don't feel at all limited by my choice of cables, or any desire or need to change them. Most of my cabling is now SR, my last purchase being a three meter length of Tesla Vortex Analog cable, which is doing just the same job for my rapidly improving analog front end.
You may get a thousand different opinions, but these do the job for me. Night and day from what I had before, and I won't mention what they were, so as not to ruffle any feathers.
That's as much as I can tell you about them. Talk to The Cable Company, they are very knowledgeable in such matters, and they carry many different brands to choose from, new and used.
Best of luck, and good hunting,
Dan