Stay in the same cable family?

Most cables in the same family have a similiar sonic signature. However, this doesn't mean you need to use all the same brand. You really have to try different cables, etc. to find that synergy. No one can say how a cable will be with your particular system.
There are reviewers who say stick with the same brand but then really, who are they to say.
I personally stick with the same interconnect brand to all sources but use whatever speaker cable I find works best. If it is the same brand, so be it.

One thing to remember: Most cable companies that make a quality product use all of their cables in systems that they reference their cables in.

Thus, most of them design their cables (AC, IC, and Speaker) to go together.

That being said... I think some companies do do better jobs making making one type of cable (AC, IC, or speaker). A few manage to make two great types of cables. And even fewer do all three cables very well. Thus, sticking with one brand of cables will not necessarily give you the best sound.

Personally, I find matching cables to be a trial and error ordeal. SOme cables that work very well in a given system will not necessarily sound very good in another system. For example, I had some Siltech G3 XLR IC's (86B I think). Anyway, I was using them with Plinius SA100 mk3 amps in mono. Plinius uses the same Siltech cable in the SA100 mk3 amps that was in these Siltech G3 ICs that I had. And I thought they would match the Plinius amps better than anything else. Bottom line was that I really preferred the Nordost Quatrofil ICs over the Siltech with the Plinius amps... Go figure....

KF

Bigtee and Tok2000 both make very good points. I have found in my system that interconnects do better from the same manufacturer, while not necessarily so with the speaker cables. However, with power cords I have found that matching different makes in the best combinations makes for a more synergistic blend in achieving sonic Nirvana. Every time I used the same power cords on all components it became too much of a good thing, so to speak. Have some fun( if you can afford it ) experimenting.

Perhaps the most important aspect for cable matching and best synergy is to keep to the same type throughout your system, i.e do not mix silver with copper. Experiment with all multistrand copper, not necessarily from the same manufacturer, and you should end up with a much more satisfying sound. It could save you a load of money in the long-run because you could feel less inclined to change your equipment every so often. Spend 10% on the equipment and 90% on getting it right!!!