I have to agree with what Shaun has just said.
Speakers are a reactive load, and the amount of current required to drive them can vary enormously. It's also entirely program dependent.
Taking an awkward load (as the Zus appear to be) and powering them with a single ended 300B amplifier is going to be, well let's just say it will be interesting.
You're only over in Chorley - give Toppsy a shout about listening to some Edingdale MkIIs.
They've been designed specifically with single ended 300 amps in mind.