Using a Pre-Out to Bi-amp

This will work if the input sensitivity of the amps in the same. Otherwise you will need something to balance them.

The amps need to have the same gain. If they don't, the drivers with the lower gain amp will have a lower volume than the drivers driven by the amp with the higher gain. The effect would be like having a balance control between the drivers, as opposed to a balance control between speakers.

This will work if the input sensitivity of the amps in the same. Otherwise you will need something to balance them.

Thank you for your answers.

What would I use to balance them?

We are both saying the same thing. If you do this you will have to make sure that the sensitivity (or gain , same thing) of the amp you are buying is the same OR HIGHER than that of your integrated amp. Why? Because the output of your integrated feeds directly into your power amp , if it is more sensitive (more gain) than your external amp there will be no way to balance their gain. The ideal solution would for them to be exactly the same but I wouldn't chance it, manufactures specifications are often inaccurate. I would buy an amp with considerably higher gain (more sensitive) because then I could even them out with a volume control in the input line. A simple one is easily constructed or get one at Radio Shack or more upscale source.