Vienna Acoustics themselves put forward a good case for not needing to bi-wire. Have a look around on this forum, there are many arguments discussions on which is better. In my personal experience I can't tell the difference.
Bi-wiring - you use the same terminals in your amp with two wires coming out, one to the high freq input on the speaker, one to the low freq input on your speaker. The crossover at the speaker is by-passed (you remove the plate connecting the two). VA say bypassing their crossover bypasses their expertise in building an amazing crossover.
Bi-amping - one amp runs the high freq part of the speaker and one amp runs the low freq part of the speaker therefore splitting the high and low frequencies. Two separate boxesmean less interference between the two and more individual control.
Pre-power - This separates out the pre-amp and power amp duties into two separate boxes. Pre-amp duties take your signal from your source and turn it into something usuable, power amp just has the grunt to make this audible. Putting it into two boxes separates the intricate part from the grunt part.
I know this is a very short description but hope it is useful.