To Benedict Arnold I would say better to solder them on or, indeed, use bare wires. If you fancy having a go yourself most hardware stores sell crimping tools. However, don't most of these plugs come with small 'grub' screws to secure the cable?
PS Did you buy those A6's?????
I always thought soldering would be better, but then someone pointed out to me that if you spend a hundred quid a foot on the cables, fifty quid each on the banana plugs, then bridge the huge gap between the cable cores and the insides of the plugs with solder bought from B&Q for under a fiver, what's the point of spending all that money on cables and plugs?
Most banana plugs aren't intimate enough of a fit onto speaker wires to avoid a huge wodge of solder in the conduction path.
Screws can come loose.
Bare wire to terminals is probably best, but it's a mess, and again, the wires can (and do) come loose over time. Which is why banana plugs (or spades or whatever connectors you use) came into use in the first place.
Crimped on bananas don't have screws to come loose and avoid that solder.
Anyway, having now started yet another round of what speaker cable / what plug / is butter really better than margarine, I'll get back to work.