Old thread but interesting topic, and i got about half way through the replies and the % of confident disinfo / complete misunderstanding of the question astounded me so much that i feel compelled to share what info i have. If i am incorrect, please let me know how and i will be glad to learn. Forgive my arrogance if you can, but if there's one thing i can't stand it's people handing out knowledge they don't have. And if i'm doing the same then tell me and i will thank you for it.
The first 2 or 3 respondents clearly didn't read the initial post/question, even though one of them pretended he had by quoting the thread starter, even though his reply clearly demonstrated he hadn't understood what he had just copied & pasted. Frightening, and possibly useful when evaluating the reliability of the info you can find here. I find this is most often the case, things like Yahoo Answers being another perfect example of totally uninformed people feeling a strange need to reply and spread disinformation, which then gets voted up and "confirmed" by a bunch of people who didn't know anything about the matter either.
I am no expert yet after a couple of searches i feel i know more than a lot of the first half of the posts here.
To say or insinuate that there is no difference between cables is about as moronic as saying there is no difference for other elements in the audio chain. If there were no difference then why use copper? Why not use something cheaper? Why not use something that doesn't oxide, for example? Of course there are differences. A cable removes part of the signal and may distort it and/or pick up interferences of various sorts. So of course there are differences.
Most people seem to think that gauge is everything when it comes down to quality (then they admit there is a difference between cables, btw). This is not true. If your + & - are far apart it will sound like ****, no matter what gauge you are using. Some smart arse said that the best cable for speakers is speaker cable. Wow, so the best paste for teeth is tooth paste, and the best laces for shoes are shoe laces. Beware, we have a genius on our hands.
Well, it isn't speaker cable, and in fact Cat5e is probably one of the best cables you can use for speaker cable, as long as you double it for each speaker. That isn't opinion or subjective, it's based on a few simple facts.
You don't want multi-strand copper for any audio cable, you want mono strand. Furthermore, you want the + & - to be as close as possible to increase rejection of interference. So the best you can do is to have a + next to a - next to a + next to a - and so on. And you want that heavy gauge so you use two cables for each speaker (i'm not talking about bi-cabling or bi-amping here).
You can buy cables like that, and they cost the price of a Corvette. OK, they will be better quality inside and shielded, but if you want cheap & decent you will use Cat5e. Cat5e is better than Cat5. Look it up if you don't know the difference. For those too lazy, click here : http://www.cableorganizer.com/articles/cat5-cat5e-cat6.htm
No, Cat6 is NOT better for this purpose than Cat5 or Cat5e. Just because it has a higher number doesn't mean it's better for audio (although, yes, it is better for digital data if you need the extra speed and want it to be more future-proof). Don't recommend that based on some sort of conditioning with product numbers if you don't know the difference.
The difference is NOT just gauge, it is mostly thicker insulation between the cores, which means the + & - are further apart in our case, since we will be using each of the 8 cores as either a + or a - (4 or each, obviously). So you don't want a Cat6 because that will actually worsen your sound. Unless of course you cable is better insulated without thicker insulation, in which case you could use Cat6 but unless you have checked that precisely then you need to steer clear of Cat6 for audio purposes.
Finally, for the skeptics who have either never tried or don't have the ears for it who still think there is no difference between cables (an assumption that is totally unsubstantiated and very unlikely when you think about it), try an average guitar cable and try a Vovox Sonorus. Night and day. Much wider bandwidth, much much less distortion, more detail, clearer, better in every way. I'm talking about the Vovox cable. Sure, it doesn't cost 10 Dollars. It's 100 € for 3.5m. But you only buy it once, and contrary to so many other cables, its construction is brilliant and i'd bet a lot it will last for decades. Spread the cost over the life span of the cable and you're talking a few dollars a year for excellent sound.
Now, if i'm talking bollocks then please let me know, call me a twat if that makes you feel better, and teach me something because i'm trying to learn here, regardless of my tone.