Biwiring

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