Never Owned a Tube Amp and Want Advice

I own a tube amp and a ss amp. Swap them out to hear the differences and enjoy both greatly. Tube amps are more 'hands on' than ss amps IME. Tube amps also have a few idiosyncrasies that ss amps do not,IMO.
Firstly, what is not really mentioned here ( at least that I could find) is that tube amps are generally more costly to run. One has to budget for expected tube replacement. Also, typically IME the amps run hotter than ss amps. ( particularly Class D ss amps) So, if heat is a concern, and it should be in many parts of the world today, then this needs to be considered. Then we have the biasing scheme required by most tube amps...( unless they are self biasing, which is the way I would STRONGLY recommend you go). I used to own an incredible sounding tube amp, but the biasing protocols were bordering on criminal! This is less common today, but still something to be very much factored in. 
Lastly, expect a tube amp to require more warm-up than the typical ss amp. With a lot of tube amps one has to wait for the tubes to stabilize before listening to music, that generally is not a factor with ss amps. In case it sounds like i am down on tube designs, absolutely NOT, but one has to expect their 'requirements' to get the best sound. ( and that sound is one that I generally think sounds better than the best ss amps, at least that I have heard!).

OP, what is your preamp? Didn't see that mentioned anywhere. My suggestion would be to get yourself a good tube pre and see how you like it with your DNA 500.

I currently use two tubed preamps - CJ 17LS2 and PL Dialogue Premium. In my listening, the CJ is more nuanced and textured while the PL is more forward and analytical. The bass is better with the PL but that may be due to a slight impedance mismatch between the CJ and the DNA - 500. More tube rolling options with the PL, which I have done and can hear with the new Tylers even though they are not broken in yet. 

I also have a McCormack RLD solid state preamp that is not really that bad except it is a bit too smooth and polite for my taste.

My expectation is that a tube amp will improve the imaging, layered sound stage, and sense of aliveness I think I hear when the treble gets better detail without sibilance. 

Thank for listening, 

Dsper

LOL I should have just asked first before adding my 2 cents!

Ok, All I can do is recommend the tube amps that, "I", personally enjoy. Like everything else this is WAY subjective. And the speakers will show the amps differently as well.
But there is more to those which I like than just the sound. And the tube power differential people have talked about? That is a "real", thing. I can't say that I understand it very well. But as the different manufacturers test, rate and also design and build differently? Your going to see a wide range of differences because of that as well!
 I have one pair of mono-blocks that only rates at 4 watts but pushes as well as any 40-50 watt tube amp that I have tried. "Sonance, Opera 300B cyber". And I will say that most tube amps that I have tried rated at 30-50 Wpc  will push as well "IMHO", as most SS amps rated for 100WPC. "Not-withstanding, Pass, Threshold and a few others"!
 My favorite tube amps overall are the "Manley Labs", ALL of the offerings from Manley sound crazy nice and are also built like a tank! And the Biasing is the most user friendly I have ever seen. Marked out for you on the top of the amplifiers themselves. And I believe they even still give you a free multimeter when you purchase them from the factory which is in Ca..
Something i have noticed though in the way you want to power your speakers for the best sound which I have never heard anyone else say before though. When I purchase/use SS amps? Headroom is a GREAT thing. It helps keep the distortion low. Keeps you away from clipping which can destroy some amps very quickly. And is just a good thing all around it seems. With the tube amps? Not so much! You want the amp max, "Where it will clip", To be near your reference listening level. Why?
 Because with a good tube amp that is where most sound there very best! But a SS amp? For most, 
"Again though",
"Not-withstanding, "Pass, Threshold and a few other SS amps, that work a little bit differently", You want that headroom to stay well away from where they clip. That for the best sound you can get from a SS amp. Because distortion from a SS amp is always just horrible noise. 
 I also have to agree with "WolfGarcia", above. The most bang for the buck", I believe would be from "Jolida", Just, now it is named, "Black Ice"!
Black Ice, also has a certain, one Mr. "Jim Fosgate", in the house now. "
"That fellow currently holds more patents than even I! And I believe he's near or even past the ,(Four-Hundred) mark now"! And those patents are all related to audio. Which now, "Black Ice" basically, has free-access to!
 And as far as tubes? they do all sound a bit different. And different as well, each in different gear! The 300B is my favorite, "Output Stage" valve to use. But they can be a bit pricey, even for new tubes currently made!

My expectation is that a tube amp will improve the imaging, layered sound stage, and sense of aliveness I think I hear when the treble gets better detail without sibilance.

Right. Should be fine. Only slight concern is when you say the McCormack RLD is too polite. Never heard that one myself. Had a DNA1, beautiful sounding amp. Very, very close to the Aronov and Melody tube integrateds. Very close in sound, very close in perceived power. Which there's the 150W SS to 50W tube equivalence thing. But in terms of sound, if you like the DNA and just want a little better imaging, layering and palpable presence, you should be able to find that with tubes. Any of the amps people are recommending should do that easily. 

Improved treble detail without sibilance is a sort of hallmark of tubes vs SS. The better tube amps provide extended treble that can seem downright liquid. The last guy to hear my system was into digital and while he was here kept thinking my system should be more cold and analytical. Only find himself yearning for that nice full round warm sound that was missing when he got home. So there's something about it that wins over even those who aren't naturally inclined. Seeing how this is already the direction you want to go its a safe bet you will find what you are looking for.