The impedance drops down to around 3 ohms over the 200Hz–1kHz region. A good deal of the power in typical program material falls in this range, which suggests that the CUB will not be particularly easy to drive.To get the very best from these Cub's.
http://www.stereophile.com/images/archivesart/wilCubfig1.jpg
This is from Stereophile’s review/measurement results, pick the right amp that can do it easy into a 3ohm load and with current ability.
Cheers George