Biwiring

...Since biwiring does a speaker crossover at the amplifier level, the crossover point may slightly change up or down depending on amplifier. You will feel biger difference in biwired setup when you turn on and listen to unwormed amplifier ( especially tube ). You will feel bigger differences in sound when the amp has unstable gain (on very low volume or very high volume operations ). The volume control possibilities of the biwired setup is more narrow: the sound may become harsh on very low or very high volume of the amplifier unlike with single wired setup.

All of that because the crossover point cannot be stable in biwired setup. Yes it will improve the sound if the amp is in stable gain operation...

...I appologize for incomplete previous explanation and in addition, for more understanding I want to say that speaker wire means a lot as well as amplifier not in terms of bucks or quality but...
1 Capacity of speaker wire as well as length -- the less length the less is internal capacity
2 Dynamic and soundstage stability of the amplifier.
If for instance you will want to get biwired Kimber 8tc which has a huge capacity -- you will double this capacity and sum it up with crossover's capacity. That can result crossover displacement + change of impedance of the speaker. What's going to be affected next -- the amplifier.
If the amplifier isn't designed for a high capacity loads (for tube lovers) -- do not even bother to biwire your speakers! For those who has solid states 12 y.o. or less it's OK. Most of the solid state amps isn't volatile to changes of impedance loads. The ones that aren't designed for that will suffer gain oscilations due to unstable impedance that will become more freequency depended in biwired setup.
I am not a professional electronic engineer but I did some research on crossover circuitry and a speaker cable equivalent circuit and will gladly read any argumental follow-ups or comments from ones that worke(d) in that field