Are Quicksilver power tube amps in the same league as VAC, VTL, BAT, ARC, ...?

Sorry folks, I didn't mean to imply that QS is one of those 'flash-in-the-pan' companies. It is undoubtedly a great company with a value-focused, no frills approach. I've owned two of their products in the past -- Quicksilver headphone amp and integrated amp. Like I said, excellent products "within their respective price brackets."

While we are extolling the virtues of Mike and QS, does he offer cap, resistor or other (non tube) upgrades? Just curious

**** But to your OP question: ’Yes’. ****

….. another reasons why, when Atmasphere speaks, I listen.

Btw, one of the nicest sounds I have ever heard from a stereo system: classic QS 60W monos driving Quad 63’s.

Yes they are great. I have three sets of QS amps: Silver 60 (which Mike thinks are one of his best), mono 60, and mini. I use the minis 90% of the time, they are amazing. I also own 2 QsS preamps, the remote and not remote. I have the last version of the non remote, it is outstanding for the money. The remote is 95% as good, and is the one I am using now for the convenience of the remote. I also  have a Parasound JC2 (great preamp), but I like the QS preamps better. I think the QS Mini's have been the best value in audio, unfortunately discontinued now. 

Great question by the OP. We all want our hard earned $ going towards quality. Most of us can't afford to play the high end merry-go-round.

In the past 30 years, I have owned VAC, Conrad Johnson, and Decware amps. I've listened extensively to ARC, BAT (sounds like solid state), Quicksilver, Lamm, Cary,  and VTL. They're all excellent, depending on what sounds you're hearing for. Some of the others spend more on aesthetics, Lamm & BAT for sure. As for better parts, I can say very confidently that VAC, CJ, BAT, and VTL use pedestrian parts. Those companies make extensive use of circuit boards as well. That doesn't make them bad, just an observation. VAC believes in maximizing the most out of the tubes. VAC is also the least friendly to using alternative tubes...kt88s almost exclusively. Not a bad thing, but also limited.
Each of these companies aim for a particular sound. Like others here have said, find what sound you like and get the best gear you can afford. If you like the QS sound, then you can spend more money on the preamp of your preference, or a phono stage, cartridge, etc.
Finally, of all the companies you've listed, I would stay away from BAT as their company infrastructure is now questionable. That means their support may not be there when you need it...and you will need it, we all need it regardless of company or amp. I'm not sure MusicDiirect is the most qualified distributor to help. They are also the least tube like amps I've ever heard.
VAC, QS, ARC, and VTL are known for their quality and service. All but QS, are also known to be very expensive. I'm not sure why given the aforementioned parts quality. On that subject, don't get me wrong, even pedestrian parts are good quality. Basically we're paying for design, marketing, and reputation.

My 2¢.
Great question and the audience you attracted have offered good advice.