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

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.  

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.

Tuning by source material is problematic IMO. I have never used a small number of reference recordings to tune my system since this not how I listen. I play all manner or recordings, all genres, all qualities over the long term. If there are shortcomings you'll hear them in time, no reason at all to speed up the process, you'll only go in circles with short term listening with a certain number of reference recordings. Having patience and quit always listening with analytical part of brain is key. Enjoy what you have, the small displeasures may expose themselves over time, only then do you make a change. And never forget one change at a time, too many variables will only confuse.