Is it best to use a 5-channel amp for biamping??

I hate to say that anything is an absolute as there are almost always exceptions to every rule. With that in mind, it would be pretty safe to assume that you should be "okay" even with goofy internal wiring in the speaker so long as you were running multiple channels from the same amp. There are some amp designs that i can think of this causing problems with, but none of the multi-channels that i know of use this approach.

As a side note, i did this for a while when the two channel amp that i use for the mains in my HT system was sent back to the manufacturer for inspection and upgrades. I had another 5 channel amp that i wasn't using, so i ran four of its' channels to passively bi-amp the mains with. Since it was from the same manufacturer, there wasn't a drastic change in sonics either way. Sean
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so Sean are you saying it's possible that using 2 of the 5 channels off the same amp to bi-amp will not deliver sonically noticeable results due to the channels all being the same maker, sonic signature, etc?

No, no, Arthur-- you'll use FOUR of those channels to bi-amp: one channel for the right woof, another for the left woof, another for the right mid-hi's and another for the left mid-hi's. Total, four.
The difference in sonics comes from driving the speakers' drive units directly, the crossover being behind the amps rather than in front. Cheers

Greg,

What do you mean by this statement..."The difference in sonics comes from driving the speakers' drive units directly, the crossover being behind the amps rather than in front"?

Are you implying that a 5-channel biamp configuration will be sonically better than a straight 2-channel instal?

Cheers

Planckscale-

Not quite; sorry should have been clearer. A little b/ground first:
Two channel stereo:
your amp receives a full-range signal (i.e. all the frequencies, typically from ~20Hz to ~22kHz) from the pre, amplifies it, and sends it as is to the two speakers, each amp channel providing a signal to one speaker. In turn, the speakers have typically 2-3 drivers on them. Each driver is designed to work best reproducing PART of the full-range signal -- so a cross-over inside the speaker filters OUT (attenuates) certain frequencies and sends the rest to each driver. The result is that the 2-3 drivers, between them, combine to give us the full-range signal that originally left the amp.

NOW, what Sean and I were saying is that, IF you were to filter certain frequencies BEFORE they actually reached the channel of the amp and then connected the amp output DIRECTLY to the driver that works best with said frequencies, the result would be far better because each amplification channel would ONLY be amplifying the frequencies that the driver it's connected to reproduces, i.e., no waste. Also, since woofers eat up most of the energy, you could have one amp channel each for the two woofers (that's two channels) and another channel each for the rest (another two channels). That is active BI-amplification and in our example you need four amp channels to do it, so a 5channel amp is indicated (you even have 1 channel extra).

HOWEVER, if your speakers have a bi-wiring facility (i.e. two pairs of connectors behind each speaker, one mid-hi, one bass) AND these are actually DISCRETELY connected to two separate filters, you can, again use four channels of amplification, each channel connected to each of the speaker inputs (four inputs, two per speaker). BUT, in this case, each amp (a channel is an amp, anyway) would be amplifying the full-range signal part of which, in turn, would be filtered out by the crossover that's inside the speaker -- SO, little improvement (the crossover is a problem-maker!) to be expected usually. Sean also adds that, since it's the same amp (i.e. 4channels of the same amp) you will have the same sonic "signature" all round... if you were to use a different amp for, one of the speakers' sections, then there would be some versatility in roughly choosing the sound you like (soem people like tubes for mid-range, but use ss for the bass region, etc).
Hope this helps!