I run two separate sets of speaker cables to biwire my speakers. (Rather than true biwired cables as you described). Having two sets of binding posts on my amps makes it slightly easier to tighten the spades down properly. But other than that, there does not really appear to be any benefit as Kal has stated.
(However, one benefit of running two sets of speaker cables, as I have done, is that I can sell them separately, (when and if the time comes), which should make them easier to sell. But then again, it did make it slightly more difficult to buy them used! But I did manage to buy two identical sets of speaker wire, the exact same length.)
Not always the same. Usually not the same. For example...
Let say the all-in-one biwire cables have four 14awg wires inside. Two pairs are combined together at the amp end, with a single 14awg wire going to each of the four speaker terminals.
You can usually buy the same speaker cable that is not biwire. It will have the two 14awg pairs combined at both ends since there is no biwire.
If you use regular non-biwire cables you will be using four cables instead of two. Each of the four terminals on your speakers will be connected to a pair of 14awg wires instead of just one. This is double the gauge of wire to each speaker terminal than when using the bi-wire pair.
Believe me, this will affect the sound. Generally speaking the higher gauge of speaker wire the better. So using four single wires that are the same wire as the biwire pair will usually be better. You listen and decide..
Didn't see a mention of this, but I have heard the reason for bi-wiring is not to increase the guage of wiring but to keep innercable frequency interference to a minimum. When a signal from your amp goes to the speaker it makes the speaker move. When a voice coil moves in a magnetic field it generates a back current that goes to the amp. Appearantly high and low frequencies behave differently in a conductor and dividing the wiring to the high and low drivers is of benefit (even though they meet at the amp terminals). It's not mentioned in your thread if your speakers have separate terminals for mids and highs. True bi-wiring is about running two sets of wires from the high and low terminals on your speaker back to the single amp terminal on your amp (not all companies design their speakers for this).
Depending on the make of wire, some manufactures recommend a double run for improved perfomance. OCOS speaker cable ( a coax design imported by Sumiko Corp.) is such an example. In this case, lower mid and bass are improved by a double run. This application essentially increases the amount of signal going to your speaker. While not a true bi-wire set up, this configuration does improve the sound. Fortunately OCOS is relatively affordable and I was able to do this. Cost can be significant if you're talking Nordost and the like. Sometimes the money is better spent using better cable instead of twice as much. Ya just gotta listen to it!
So bi-wiring is about the physics of two way traffic in a speaker wire between the amp and the speaker.
Im also contemplating bi-wiring my speakers. Some cable makers claim that they sell true bi-wire, which I take to mean the equivalent of the four separate wires described by Kurt tank but wrapped in one or two separate sheaths per speaker. If I decide to go with such a cable, Im certainly going to question the manufacturer first to be sure that the wire connected to each speaker terminal is not half (the gauge) of the wire connected at the amp terminal.
My question is, from an electrical interference point of view, is it better for the wires to be packaged in two sheaths or even a single sheath per speaker, which looks neater and may reduce the chance of tripping over wire, or should the four wires to each speaker be kept apart?
Well here's what I just learned. Two sets of cable to bi-wire has the advantage of being able to compare bi-wired to single wired. In my case single wired with matching jumpers actually sounds much better on my speakers. My last speakers were far better bi-wired, so I think it's important to hear high quality cables on your speakers both ways to make an informed decision, which you can't with the bundled run of bi-wire. As always, YMMV.
You have to compare apples to apples here.
Whether your biwire cabling is two separate sheaths or one sheath with two cables inside, the wire gauge at the amp end is going to be the sum of the wire gauges at the speaker end.
The OP asked if the connection at the amp end was better made to a single output post (per channel), or divided between the two output posts available. Kal's monosyllable was correct IMHO, electrically and sonically.
The best reason to use both posts is convenience and secure connection. If you have two sparate cable runs, they connect to the speakers on two different posts, and the nuts on those posts are easy to screw down tight. When you connect those two wires to a single post on the amp, they may not be easy to tighten and keep tight, especially if the wires are heavy and the connectors are large spades.
If, like me, you have a single, two-in-one biwire cable (a "shotgun" configuration), the two wires are joined together at the amp-end connector. Connecting this to a single binding post is easy.
Two sets per each channel in the amplifier may have a different purpose and meaning such as speaker impedance ranges(I used to have Nikko Alpha amp where I have to choose the right combo of a binding posts for a specific speaker),
a capability of connecting more than one pair of a speakers(switchable or playable at the same time)...
Otherwise if it somehow may make difference in the speaker side on the amp side it's realy no difference.