Hi Pierre, sorry have been rather busy the past few months, no time to reply.
Each item in my system has a history and came about from listening to them in different systems and ultimately in my own before it replaced the older unit. So it's difficult to say which 2 items made the most difference. They all did and in such a significant way that I bought the item.
That said, I would have to mention that it was vibration control that allowed the components to perform to their peak abilities. And secondly room shape is important too - I used a room shape calculator to get the basics right then sort of guessed the rest. I choose to follow one of the Louden room shape ratios (1:1.4:1.9) which satisfies the Bolt, IEC and EBU good sound design ratios also.
A good room shape allows you to find a good spot for the speakers (this is still very much a requirement) so they can play deep smoothly without boom. Good choice of room finishes allows the HF to play well. And good vibration control allows your components to show all they can do.