A few people have said tht MA are bright. They can be but that's more likely to poor partnering and no room treatment. They are very musical and can be harsh when not partnered correctly. Otherwise I find them to be great!!!
One solution is to budget a certain percentage of your amp/speaker price to cables. That way you don't waste money on insignificant upgrades which have little improvement/price ratio. I.e. if your speaker cost R5000 be prepared to put in 10%/15%/20% of that price on good cables
All those amps look great. I have experience with Onkyo and they are known to go well with Polk.
Don't forget your speaker cables - they can directly affect the sound of the speaker. PAPPA3 has some good ones at very good prices at the moment. You can even buy a long length and cut it to...
Bass traps in your corners (even in the ceiling corners if you can swing it past the missus). Absorption panels at deflection point to catch HF and midrange where necessary. You need both since the serve different purposes. Unnecessary bass traps are overkill and will be unsightly. Be careful...