If the upper end has impedence of 8 Ohms and the amp puts out 100 w/ch at 8 ohms, and the lower end is at 4 ohms, and the amp 200 w/ch at 4 ohms, will this result in a problem in the resulting aural output than would have been experience with a single amp?
No, that won't result in a problem. The proportion between the amount of current and power drawn by the speaker at high and low frequencies in response to a given amplifier output signal voltage will be the same regardless of whether the current and power required at each of those frequencies are provided by the same amplifier or similar separate amplifiers. This assumes, of course, that identical signals are provided to the inputs of both amplifiers, and that the amplifiers are either identical or their gains are matched in some way.
If you do end up biamping, since you would be using two identical amplifiers you may want to also try a "vertical" configuration, in which the two channels of one amplifier drive the high frequency and low frequency sections of a single speaker, respectively, and the two channels of the other amplifier drive the high frequency and low frequency sections of the other speaker, respectively. Compared to the "horizontal" biamp configuration you are proposing, the vertical approach would have the advantage of having the same signal going through both channels of a given amplifier, potentially reducing interchannel crosstalk.
In general, though, I agree with the others that simpler is usually better, and that a single higher-powered amp will often be a better solution.
Regards,
-- Al
