PrimaLuna Evo 200 underwhelming

You can get a great sounding integrated SS. It isn’t the technology, it is the actual make and model design and execution. You can make generalizations that tubes sound better, but it is not true in all cases, and this is even more apparent on lower efficiency speakers. 
If you really like a speaker/amp combo, be happy and don’t worry about the technology generalizations.

I am in the minority here but I believe in KISS. No messing with tubes, heat, etc. You already went KISS with integrated vs. separates, now just give a really good SS a chance.

 I see you have, or are considering sending back the PrimaLuna. If you haven’t already, I recommend you don’t - at least not until you give the KT120 or KT150 tubes a shot. Will cost you about $200.00, but from experience I can tell you, that with demanding speakers, they will shine far and above the stock EL34s. While the EL34s can be magic with very efficient speakers, they fall short with even slightly inefficient speakers.
+1 @ hardens "I recently rolled in a set of KT120 power tubes and noticed more detail from lows to highs and more power and weight in the bass".
I am driving my quite challenging Maggie 1.7s with a Rogue Cronus Mag. II, running Tung-Sol KT-120 tubes and it has no problem driving them to any volume I care to listen to and the resolution, detail and stage is incredible.
I think you owe it to yourself and your very nice Robson speakers to give it a shot.....Jim

@jhills Where do you get the KT120s and what made you choose those over the KT150s?

I am driving my quite challenging Maggie 1.7s with a Rogue Cronus Mag. II, running Tung-Sol KT-120 tubes and it has no problem driving them to any volume I care to listen to and the resolution, detail and stage is incredible

.

A bit of what keeferdog referenced. I've rolled several matched quads through my MAC 240, Svetlana, Sovtek etc.. they weren't even close to the Tung Sol 6l6GC reissues i have now. Even better than a mismatched quad of RCA's (questionable vintage). 

@golfnut2 "I will have anther go at swapping the input tubes, they solid though. Apparently the was ex display and never used, it certainly looked untouched out of the box. Just answer an earlier question, the Robsons sounded great through a PL Prologue Pre amp with Cyrus X Power amp. In hind sight, maybe I should have gone for that combo and it may have been a whole different story."

golfnut2, Ask Upscale to replace the input and output tubes, both. See what they say. Who knows what this demo was before you got it, could have been a return from someone else who did not like the sound. EL34s can sound great with the right efficiency speakers.  Maybe not so much with lower efficiency veiled over speakers. And, you may not be an EL34 type of listener and closer to liking the sound of KT88+ output tube sound as many have already suggested. If they don't want to help you on tubes, just return it. I bet the right small signal/input tubes paired with good KT88 output tubes would be more to your liking.   Best of luck.