[Yamaki]

At the McIntosh end, there is a locking ring on the terminal. You need to loosen it to open up the connection fully. It is the top knurled ring.

On the speaker end I'd check that connector for either push pull or twist adjustment. I'm not that familiar with B&W connectors but as with most speaker banana plugs, like on my Aerials, you normally loosen the connector ring by twisting it to the left, the inserting the plug, then tightening the ring.