I'm afraid your questions are not very well focused, making it difficult to answer them.
Also, not many of us are informed of what gear is available outside of the US, so you would need to let us know which manufacturers are available
Does saying you want the "very best" mean that you have no price limit?
Is there a model number for the sub he has?
In the mean time, here is an article discussing some of the current AVR's which you/your friend might look over to familiarize you with some of the considerations you might have:
https://www.lifewire.com/best-home-theater-receivers-1300-and-up-1846334
Honestly, any of these would probably work well, and there is little reason to spend so much, IMHO!