Sandro,
These systems are rather basic in thier design.
All they really are is a bunch of Mono-phonic speakers all hooked up in Parallel.
The reason for the 70V (or the 110V, we use here) is because of the long runs of speaker wire involved.
All the transformer on the speaker does is isolate the speaker from the 70V line voltage and also match the speaker to the line, hence the tappings. [Linked Image]
I ran my system in Cat-5e. [Linked Image]

[This message has been edited by Trumpy (edited 05-15-2005).]