jo1mtb, it's good that you are comparing different pces in your own system for your own taste.
So many factors come into play, rest of your system components, room etc. so others will differ.
Put in a Ref6 or any other component and your comments will change again, reposition of your speakers - add room acoustic panels - doing any of these what you are currently hearing will change - it's never ending.
Your comments above referring to a 75 saying;
"I felt/and do feel that the 75 is a bit bright (like a gold gilding) on the high highs (like symbols in rock music)." non SE version
My speakers are 107 db and if such was present would be easily heard but there are no such findings - my set-up is totally different than yours but clearly shows system dependant.
Personally what you are describing is what I here when listening to your version of speaker - the series 2 not so which is my preference.
So many factors - for sure it's a never ending journey. Personally I would have upgraded from your Ref3 to 6, there is one currently up for sale and paired it up with the 75SE - break both in and enjoy! Work on the rest of your set-up and then get a 150SE say in years time or so to compare if you find you are still missing something.