Do high dollar mono blocks truly improve the Sound Quality over the mid tier amps

In your system I’d first look at a better streamer from Innuos, Aurender, Grimm, etc.  The Zenith is really good, but I think there’s a good bit more to potentially be had there.  Just my $0.02 FWIW.

I don’t think upgrading those already excellent amps will make a noticeable difference. Better speaker placement, better room, better recordings would imo make much bigger differences. It’s my belief once your amp/amps are very well made and powerful, differences beyond that from upgrading the amps are extremely subtle.

Obviously changing speakers would change your sound. But you have great speakers, so it’s unclear if changing them is an upgrade or not. 

on a serious note: I am sure you can get a different sound that you enjoy more. I don't know how you go up from where you are now.

Wow, beautiful system and house. What a wonderful place to enjoy music!

If you would like better performance I would look at upgrading your streamer and preamp. That is what looks to me to be constraints on your outstanding system. Look at the top of the line Aurrender to put your digital end in line with the rest of your system. For preamp I would look towards Audio Research or Conrad Johnson. 
 

A bit of a different point of view on @atmasphere ’s comment about price. Audio companies have different house sounds (“intentions”) and by moving up in cost of product the house sound is invariably improved. So, in this sense you get what you pay for. I have never heard a lower level component sound better than a higher level one. For instance moving from entry level Audio Research preamps to their flagship. However, you might prefer the house sound of, say Boulder better. So, if you don’t have a wide range of exposure you could consider a low level ARC preamp to be better sounding that a top tier Boulder. 
 

Alternatively. You could add a high end component to your lower tier system and it could sound bad because it just isn’t synergistic. But within sound categories you universally get better sound the more you spend. I’m sure there is a few exceptions or special circumstances, but in my fifty years I have not stumbled into any real concrete examples. 

Tried to focus the discussion on amp upgrade to folks with direct experience rather than a general system critique. @ghdprentice  thank you for your kind words.  In response to comments on my pre and music server I will offer this.  I have the new Innuos Zenith NG on order arriving in a few weeks.  As to the pre I recently sold my VAC Signature Mk IIa (SE) which was in the system.  I preferred the pre in my MSB Reference DAC which has one additional balanced input that I run my phono pre into.  Room acoustics are great.