Beginner looking for guidance into tube sound.

If it is so important to add some "tube sound" then yes a preamp is more in your budget. In the longer run however I would never do it, not on your budget, because separates are so much more costly for what you get. My budget for example is a lot more and even at my level I still do not see the advantage of separates. 

What you are going through is exactly what I went through. Only for me it was around 1973. I had paper route money, and a bicycle to take me to Radio Shack, where I devoured all I could read and picked the brains of everyone there who knew anything. 

Anyone who does this a couple things become clear: if you buy inefficient speakers there is not enough power in the world to make them sound good, but you can spend a fortune trying. If you buy separates you can spend a fortune trying to make them sound better than a good integrated amp, but in this case you might at least get there eventually, if you have enough money. And you can try and stuff everything into one box, but while it may seem to save money one thing interferes with another and so it just never works.

Therefore, high sensitivity speakers (which is kind of arbitrary but never anything less than 92dB) and an integrated amp is the way to go. Until and unless you have piles and piles of money and a burning desire to spend it all this is the way to go.

If you get something like that Decware integrated you will absolutely have freaking mesmerizing captivating amazing sound. You will also not be able to play real loud, at least not with your current speakers. You will also not have real powerful bass, again not with your current setup.

But you will have an absolutely awesome sound from what you do have. That is the tradeoff. The fact of the matter no one will tell you is really high quality is not expensive. What is expensive is extending that really high quality into high volume range, especially when it comes to bass.  

But for bass the solution is a DBA. So if you are smart you wait and make do with everything except bass and high volume. Then when you can afford quality speakers you match that Decware with some Tekton, man now you got something. Then when you have another $3k you add a DBA. Now you pretty much have it all. But in stages, and so it took some time. But you had superb quality from the beginning, just not in the deep bass high volume ranges.

That's the compromise. Maybe on the other hand you want high volume now, and that is more important than quality. Or whatever. It is after all your system. Prioritize and plan accordingly.

The most important thing when trying to do high sound quality on a budget is to understand it is always all about compromise, and then figure out which compromises you are most able to afford and live with. 

For example, the path you are on looking for Quicksilver monoblocks the compromise is it is not a budget path. Separates have all the same needs as any other component- interconnect, power cord, springs, etc - but for all that you get only a power amp. Very good choice if your system budget is into six figures. Very poor choice if it is in the low four figures. 

The other tradeoff people make is quality. Low end budget gear falls in this category. You get tubes yes, but they don't sound very good because with tubes quality is what it's all about. Not just quality of tubes either but quality of transformers, caps, and other components even more so. Sometimes the quality compromise is they are not very good parts, other times it is just they are not very well made. 

There is a third tradeoff, and that is for you to put a whole lot more effort into understanding what is going on, prioritizing your personal needs, and then making a hard cold choice as to what really matters to you. 

If you can for example compromise on speaker choice, instead of buying whatever speakers you like and then trying to find an amp that will run them, you might choose only very high sensitivity speakers. Because they don't cost more, but they save you money by not needing a lot of watts. Then you find there are very low power tube amps that sound absolutely divine, do not cost an arm and a leg (because, low power) and really the only compromise is not high volume or great earth shaking bass.  

It is always a compromise any way you go, and yes any amount of money too. You already put yourself in a box with those Monitor Audio speakers, at only 90dB they are too low for many amps that would be an absolute dream had you only known to buy something like Tekton Lore Reference. At half the price, but 6dB greater sensitivity they cut your amplifier wattage needs by 75%. Yes you need only 1/4 as many watts to drive them to the same volume as your Monitor Audio. Sound better, too. 

If you are in love with those speakers, great. Just know they are forcing you to consider only high power amps, and those cost money. Low power amps you can get the insane good sound you seek, just not from those speakers. https://tektondesign.com/product/full-range-speakers/mid-towers/lore-reference/#color

With those you can run this, and it will play Lore as loud as your current speakers will with 50 watts. https://www.decware.com/newsite/SE34I.htm

See what I mean about compromise?