Sigma Drive does not have to be used to enjoy this amp.

However, all of the answers are available here:

http://www.cieri.net/Documenti/Kenwo...al%20Guide.pdf

In short,"Kenwood's Sigma Drive has been widely acclaimed as an effective means of providing optimum speaker control and an extremely high damping factor right up to the speaker input terminals. In addition to the normal speaker leads, a special 'Sigma' connection feeds distortion products caused in the speaker wires and in the speakers themselves back into the amplifier's NFB loop for effective compensation. The result is a total control over the speaker's behaviour, with optimum damping of unwanted speaker movement."

This is how you use the Sigma Drive, if you wish: