Hi Sam,
Those Yamaha amps are good bit's of kit. I used an AX620 up until a couple of years ago. Seen as you preferably want good stereo and 5.1 performance I'd consider getting a decent pair of bookshelf speakers to use on the front L and R channels and then get some smaller satellite speakers for the centre and rears and a sub. That way you can setup one of the inputs on the amp to be 5.1 for movie and another as stereo for music and get the best of both worlds with the better front speakers. I'm sure I've seen some small satellite speakers available individually or as sets of three but I can't remember the brands off the top of my head. I'll try and find some examples.
Source: Apple TV 4K - DAC: Beresford Bushmaster Mk II - Preamp: CI AudioPLC-1 Mk II - Power Amps: Musical Fidelity 550K mono blocks - Speakers: Wharfedale Opus 3 - Cables: Mark Grant etc - Misc: Belkin PF30 mains filters.