G'day mate! Welcome.
Many here aren't enamored of Bose for the spec and cost. I tried briefly with an early Acoustimass system and got rid of it almost immediately (but sold it to a friend who uses it still, some 20 years later, or is it 30 now? yeesh! ). What they call a "sub" is particularly pathetic IMO. I've seen measurements of frequency range gaps between the bass module and satellite speakers, too. Generally Bose doesn't allow for proper reviews without threatening lawsuits from what I've read so hard to get good information on them let alone measurements. They tend to have relatively high price tags for the performance in general (speakers and subs let alone electronics). They aren't always true components either so changing them out down the line can be an issue depending on model. I haven't looked up your model nor am familiar with it.
Really not familiar with your particular choices available, I know several brands of speakers I might recommend wouldn't be available in Australia. For some of the major brands I'd also think your pricing is higher there from many comments I've read from Aussies. So some input from your side as to available speakers and sub brands would be a good thing. Note the only good reason generally for same brand of speaker and sub is matching aesthetic, often speaker company subs aren't as good as those from the sub specialists.
When you say you have rear mounted speakers, is that literally on the back wall rather than the side wall where surrounds normally go?
Nothing particularly wrong with that model of Yamaha avr that I know of, altho I know here at Audioholics the A860 didn't fare too well. Speaker choice has more to do with choosing appropriate amplification than the other way around, otherwise an avr is mostly about connectivity/feature set. You have 4k tv? You want Atmos audio down the line (ceiling mounted surrounds essentially)?
What kind of AUD budget we talking about here (if you just say dollars or use $ people will think USD).
Cheers
