Fine tuning the system. Where do you start and how do you proceed ?

@inna ...Now digest all of the personally pertinent parts of the above...

And go have fun following your muse... ;)

Tuning and fine tuning with tubes is a great way to improve the sound or simply to make it slightly different. It can be like putting different strings on the same acoustic guitar.

Playing with isolation/resonance control devices could be fun, but I don't have energy and funds to approach it seriously. This would require tremendous work to find the overall best solution.

When doing fine tuning it would be wrong to dissect the sound. This is the final polishing, the sound is already excellent.

The system will only sound as good as the room allows.  Otherwise you are putting Turtle Wax on a car that only has primer and no paint on it.  

Highly recommend you look at BACCH4Mac with room correction... game changer, biggest overall improvement over anything else I have tried.... 

https://www.bing.com/search?q=baach4mac&cvid=5485145f7ca14770a71652ade00b4723&gs_lcrp=EgRlZGdlKgYIABBFGDkyBggAEEUYOTIGCAEQABhAMgYIAhAAGEAyBggDEAAYQDIICAQQ6QcY_FXSAQg4NTI4ajBqNKgCALACAQ&FORM=ANAB01&PC=U531

It's all fun enjoy it the advantage of big cities is you could borrow or listen to fellow audiophile stuff.i don't have that luxery.our nearest audio store is 3.5 hours away.the cabel company has a loan program I have not tried that yet but maybe soon.