Mthieme: It sounds like you are confusing bi-wiring with bi-amping.
Bi-wiring allows two separate wire paths from the same amp to the speakers. One set of wires carries the signal fed to the low frequency section whereas another set of wires carries the signal fed to the high frequency section. There is no need for multiple line level signals as you are only running one amp. As far as how wires for bi-wiring work, you can have physically separated wires for each frequency range or have one bigger cable with internally separated sections for each frequency range.
What i think that you are asking about is multi-amping. This does require multiple line level signals. If bi-amping, you would need two line level signals for each channel. If Tri-amping, you would need three output signals for each channel, quad-amping requires four for each channel, etc... Some preamps do offer multiple line level outputs on their back panels, but the most i've ever seen were two jacks per channel. HT processors may have more than this depending on their design.
If you are passively bi-amping, you can simply run one set of interconnects from the preamp to the tweeter amp and the other set to the woofer amp. If you don't have multiple outputs on the preamp, one would have to use some type of signal splitting device, commonly called a "Y" connector or "splitter". The signal can be split multiple times, but one needs to pay attention to impedances and how things are hooked up when getting "crazy".
The other alternative when multi-amping is to go "active". This places an electronic frequency dividing device between the preamp and all of the amplifiers involved. This device has one set of line level inputs with multiple line level outputs. Each output is designated for a specific frequency range. The circuitry inside of the device actively separates the signals based upon their frequency ranges and sorts them accordingly. These divided signals are then fed to the appropriate output jacks which in turn are fed to the appropriate amplifer for that frequency range.
This type of "active" signal dividing can provide many benefits over a system using "passive" multi-amping for multiple reasons. However, it is also more costly and more complex to get dialed in. I would not suggest such a system to someone that was not interested in "tinkering" quite a bit. If one does have tendencies towards that type of nature, the results that one can obtain can be quite phenomenal. That is, IF it is done "right" and this does take a LOT of effort.
Personally, i am actively tri-amping one system and actively bi-amping another. Another one of my systems is bi-wired. I know that this can be somewhat confusing, but i hope that this cleared things up for you a bit. Sean