Probably the easiest and most flexible way is to buy some stacking (or stackable) banana plugs.

There are a couple of main types - one where you stack plugs into the end of the previous one, and another where there’s a 4mm hole in the side. The former can take up a lot of space behind the amp, while the latter typically won’t.

I’d want to be sure that there is enough power to drive 6 speakers from one Sonos Amp. The only speakers I’m familiar with that does auto load matching is some Sonance Architectural speakers. 

The stacked plugs is one option, another is to use a short, several inches, section of the heaviest wire that will fit your plugs in them and then splice the incoming speaker wires to the fatter wire.