Having recently purchased some B & W speakers, I was told that the manufactuer recommended biwiring so that's the route I took. I'm sure there are lots of opinions as to whether biwiring adds any real benefit. I'm thinking about upgrading speaker cables and was wondering if I would be just as well off going with better quality single runs and utilizing jumpers at the binding posts ?
This could be a difficult question to answer unless one has no faith in bi-wiring capabilities. While I am a believer in the benefits of bi-wiring I am a strong supporter of using the best cable one can afford. Its my opinion that a much better standard cable (with good jumpers) will afford you better results than using the same value (you insert the dollar amount here) than bi-wires. I would say set your budget amount and audition comparably priced cables - 1 set of "regular" and one set of bi-wires - only your ears will count and of course its your wallet that will dictate just how deep you want to wade in... Audioadvisor offers 30 day returns and the Cable Co. does loan out cables (and is reported to be quite knowledgeable) for a small cost that I do believe can be applied to the purchase.
There are lots of posts on this topic, and from what I gather most folks believe that biwiring provides some benefit over a single wire. However, in my limited experience with bi-wiring a pair of ProAc's using MIT T-2 cable, I was rather unhappy with the results when compared to single wire. It may have been my particular installation, which at the time still needed to find the right balance of interconnects, or may be just a problem pair of cables, but the results I experienced were definitely better with the single wire cables. I found that the biwire cable presented a very unbalanced sound (overly accentuated lows, recessed mids and mid bass, and peaky highs with roll off at the extreme top end), which I didn't experience with any of the single wire cables I tried.

Anyway, as I said, lots of people seem to have had good luck biwiring, so it may be worth a try. I have been planning for a while to give biwire cables another run now that the rest of the system is properly wired, but summer seems to have increased my weekend laziness a bit ;-). Soon though...

Adding jumpers at the speaker posts only moves the signal separation point from inside the speaker to just outside the speaker. In a a true biwire setup, the separation is at the binding posts of the amplifier. I have rewired my Maggies so that the bass cable only 'sees' the bass network and the mid/hi cable only 'sees' the mid/hi portion. This is the real benefit of biwiring... the speaker crossover begins at the amplifier. The results can be debated, but I noticed a more seamless and open sound. The soundstage also had a deeper presentation. I am sure there are fellow B&W types who can recommend speaker cables. I would also like to hear their opinion on biwiring.
...Since biwiring does a speaker crossover at the amplifier level, the crossover point may slightly change up or down depending on amplifier. You will feel biger difference in biwired setup when you turn on and listen to unwormed amplifier ( especially tube ). You will feel bigger differences in sound when the amp has unstable gain (on very low volume or very high volume operations ). The volume control possibilities of the biwired setup is more narrow: the sound may become harsh on very low or very high volume of the amplifier unlike with single wired setup.

All of that because the crossover point cannot be stable in biwired setup. Yes it will improve the sound if the amp is in stable gain operation...
I don't understand how there can be a crossover effect at the amp binding posts. Can someone please explain?
I'm not sure you got that exactly right, Marakanetz. The same amplified signal is sent down both runs of a biwired speaker cable--there is no crossover in the cable itself. The speaker binding posts are wired separately and pass the signal along to their respective drivers. There is no crossover anywhere in the chain in question (there could be one downstream of the speaker binding posts if it's a three or four-way speaker, but that's beside the point).

My advice--if you're a believer that not all cables sound the same--is to go with the biwired speaker cables. Most jumpers are made of relatively cheap material and not something you'd want in your signal path. Unless your jumpers are made of the exact same materials as your speaker cables (not likely) that will result in some degree of degradation of sound.
Maybe the best thing for you to do is try it yourself. As a experiment you could pick up some standard 12 AWG speaker wire and compare using single wire and biwire. (Use a short length of 12awg as a jumper for the single wire.) If you find bi-wiring works in your system the second choice is how much do you want to spend. If you cannot currently afford the cables you want, start with a single pair and then save up for the second pair for biwiring. This assumes you do not mind having two cables running to your speakers. The combined biwire cables are a cleaner package. Some people use a different cable for the high and low drivers. (MIT biwire cables actually have the cables marked for high and low frequency.) I do biwire my B&W speakers with good results. Happy listening.
...I appologize for incomplete previous explanation and in addition, for more understanding I want to say that speaker wire means a lot as well as amplifier not in terms of bucks or quality but...
1 Capacity of speaker wire as well as length -- the less length the less is internal capacity
2 Dynamic and soundstage stability of the amplifier.
If for instance you will want to get biwired Kimber 8tc which has a huge capacity -- you will double this capacity and sum it up with crossover's capacity. That can result crossover displacement + change of impedance of the speaker. What's going to be affected next -- the amplifier.
If the amplifier isn't designed for a high capacity loads (for tube lovers) -- do not even bother to biwire your speakers! For those who has solid states 12 y.o. or less it's OK. Most of the solid state amps isn't volatile to changes of impedance loads. The ones that aren't designed for that will suffer gain oscilations due to unstable impedance that will become more freequency depended in biwired setup.
I am not a professional electronic engineer but I did some research on crossover circuitry and a speaker cable equivalent circuit and will gladly read any argumental follow-ups or comments from ones that worke(d) in that field