If a speaker requires that all four binding posts be hooked up in order for all of the drivers to operate properly, one can passively bi-amp with out a problem. There is one hitch to this though...
If the speakers are improperly wired internally AND someone is using two different amps to run their speakers, you could run into big problems.
The reason that i mention this is that this is the exact situation that we ran into with my Father's speakers when we pulled them apart. The lower midrange driver was "cross-wired". In other words, the positive of the midrange was connected to the "high end" binding posts and the negative of the midrange was connected to the "low end" binding posts. Luckily, my Father never tried bi-amping his speakers.
What this would have done is tied the output stages of each amp together electrically. Depending on the design of the amps and the voltages involved, this could result in "smoke". While this was obviously a mistake from the factory, it would have been a costly one for the consumer. In such a situation, i can picture someone standing there with one wire in each hand and blackened soot all over their face saying "what the hell happened???".
In this type of situation, i sincerely doubt that the manufacturer of the speakers wouldn't have stood behind their mistake and paid for the repair of one or both amps. The really bad part is that someone might have the amps repaired and not realize that it was a problem with the speakers, possibly repeating such a disaster.
As such, i would suggest connecting just the high frequency section of the speakers in normal fashion and make sure that all the drivers work as they should. When your sure that this works fine, connect the low frequency section and make sure that all of the drivers used in that frequency range are working okay. Once you've done that, hook the positive to the high end section and the negative to the low end section. You should have silence. If it is silent, connect the negative to the high end section and the positive to the low end section. That too should be silent. If you get sound out of either of these "non-standard" wiring configurations, the speaker has internal wiring problems or is not a "true" bi-wire / bi-amp capable design. Sean
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