High End System Building. How important is the matching, cabling and room? Thoughts ?

Right. There are only two places where matching is important, cartridge to tonearm and amp to speakers. Cables, depending on their purpose, are either good (sound like nothing) or bad (sound like something). There is nothing in between. 

If you have a bad room you have a bad system and the solutions are to use headphones or find another room. 

A dealer's job is to make money. Survival is always #1 with humans. I know only one dealer who could care less. His shop is a retirement gig and he is all set in terms of finances. Not that other dealers are not OK to deal with but I have never experienced a dealer telling anyone to go to another dealer to buy the competition because it is better. I worked in that system for 5 years from a big box store to the highest end store in the neighborhood. The only difference was the degree of sophistication. 

erik -squires is absolutely right ...

Nothing will replace room acoustic power of transformation for the worst or the better ...

No wave guide or near listening field will cancel room acoustics power potential , i do the two i am in near listening field and i redesign my active speakers tweeter wave guide and porthole by the way ...😊

Knowing the speed of sound and room dimensions it is preposterous to claim that reflected waves will be discounted because of near field listening in a small room ...

I hear modifications in my small room even through nearfield listening ...And my directed wave guide tweeter are at 3 feet or few inches less from my ear ...

Acoustic passive treatment and active controls of the room are the most important factor ...

After that electrical noise floor of all components and of the room and of the house together ...

Vibrations controls of the speakers and resonance control in third...

Cables come way after that ...( save if your cable are horrible and even with horrible cable , it is certainly and probably fouth factors so much impactful are the others )

i know for a fact that most people had never go through extensive room acoustic modifications than they think acoustics controls is a cherry on their gear choice cake ...

Completely false...

The gear choices matter less than the acoustics.... The only exception would be comparing my low cost active speakers, so good they are modified with a Revel or top Tannoy speakers...Here the extreme choice between low cost and higher cost speakers matter AS MUCH as the room controls... But only in this case , for most people average speakers mid-fi choices , even upgrading the speakers will be in many case way more astounding than redesigning the room acoustic...But most people cannot even had a dedicated room , this is why they are forgetful of the acoustic huge impact , they never experie4nced it anyway ...

Room acoustic for me is way more than buying few panels by the way ...

Anyway i know that most dont know and will never know...A dedicated room cost too much, even me now i am in a smaller one i could no more design at the le4vel of my past one ...Near listening field ask for room acoustic but not at the level far listening field asked for to be optimal for sure ...

Because i could not imagine it BEFORE doing my many years room experiments with resonators and others devices i understand why most people can think that other factors matter more ...But truth must be told...

Acoustics rule everything in audio...Not the reverse so important it could be ...And acoustics concepts exceed room acoustic design ... I modified my porthole design with acoustics concepts ...

Nothing is as important in getting to done as the room and it’s treatment. You can go round and round with speakers, and cables but when you get the room sorted, you are on the express train to done.

As for cables, after a lot of playing and listening I’ve settled on pure silver interconnects and Mogami speaker cables. Everything else I’ve heard has been subtractive.

@jacobsdad2000 now you are talking.  Some people think I’m dissing lesser equipment and that I’m dissing the importance of the room.  I have slowly climbed up the chain through the years.  I have seen cheaper systems with proper cabling and tweaks  that are matched correctly mollywop more expensive systems. Synergy is really where it all starts. But I have found that when you do have properly matched high end systems with proper cabling in the right room  that also have synergy it is truly sublime. Nothing against anyone’s set up but that’s my personal experience.  I have had access to a lot of great gear and I have learned how to get  really good performance out of said gear. 

the room is paramount, as it couples with the chosen speakers

There is a  false marketing tactic on the rise from the dealers these days. Dealer sez, "Hey, unsatisfied/disgruntled audiophile, I'll take the guesswork out of everything for ya. I will create the synergy of components for ya. You go plop it down in your room and magic just starts to flow like the Niagra. Just remember, that's the greatest perk of going to the knowledgeable dealer!!"

Really?? Let us explore that lie for a minute...How the flip did he create that "synergy" for ya again?? He put together a mix of components for a specific "synergy" that worked in his room! You take that synergistic wonder and plop it down in your room and it sounds nothing like what he heard in his room. His tastes are very different from yours. So ...even if he genuinely tried to build a synergistic rig for you, it will be way off in your room for your ears. 

Most often, his "synergistic build" is a list of sht that he either finds very hard to move (rarely sells) or some other sweet saucy deal he's got going with specific vendors. It is just business most of the time. Even if he forgot about maximizing his wallet for a minute and made a genuine effort to build a rig for you, he will be way off (in execution).