Depending on your Speakers the Cary Audio CAD300SEi can produce what you are looking for.
I myself can name just one – Octave Audio V 70 integratedWhich output tubes did the Octave V70 have? The most liquid sounding tubes I had in mine were the EL 34's and original Tung Sol 6550 black or grey plates. The EL 34's did lack the lows. The TS 6550 have much better lows. Ei KT90 type 2 or 3 is also very good. I didn't care for the KT 120's when I upgraded to the V110.
That said Octave has released the V80SE which uses KT 150's. I have heard KT 150's in an AR amps and they sounded extremely good and realistic.
As Pbnaudio mentioned a lot will depend on your speakers. When I had Dyn C1's the TS 6550's were the best sounding. But when I upgraded to Raidho they were too warm and the Ei KT90's were the best.
VAC is in a completely different league than Primaluna. PL makes good entry to mid level tube gear, where VAC approaches state of the art. Also, the build quality is better and they really stand behind their products. If you have a problem after the warranty runs out, they usually fix it for free anyway.
If you don't want to buy an older model, I'm sure you can find something just as good, if not better, in they're current lineup.
The VAC amplifies are indeed excellent but they are not integrated amps."
I know. I own one myself. The OP didn't ask for an integrated, but if that's what he's looking for the VAC Avatar is integrated. I'm not sure if they make it anymore, but they probably have equivalent in their current offerings.
I listen to piano stuff a lot…jazz and classical…and KT150s (with GL 12AX7s and NOS Mullard 6201s) in my Jolida 502p do an amazing job of allowing tonal accuracy with vibrant mids…note that higher expense does not guarantee better performance which Primaluna and Jolida can prove all night…both have excellent build quality, and does anybody think Kevin Deal or Mike Allen won't stand behind their stuff? You can usually get either guy on the phone immediately. I know that if a company charges 10 times the cost of another for the same tried and true tube circuits you can think there's more mojo…especially if you're the one paying for it.
In addition to VAC, the amps with the most liquid midrange I have heard have been from Jadis, particularly their JA 30 and 80 monoblocs (especially when used with EL 34 tubes) and their Orchestra and DA 60 integrated amps. Jadis gets the midrange right. And I agree with Wolf, the Primaluna integrated amp is a terrific amplifier with a beautiful midrange.
If you want liquid midrange nothing tops triodes...
Getting power from triodes is an issue though but much depends on the implementation of the amplifier. So far there has been no mention of the speakers used which will play a big role in this. The match between speaker and amplifier is going to be really important!
Another vote for VAC - famous for one of the best midranges in audio at any price. The obvious point being made earlier, was that the Manufacturer/Owner of the Company (VAC) goes out of his way to provide exemplary customer service and always has. Using dealers for comparison misses the point. I'm sure they provide excellent service as well. Its not about the dollars, but the position of the person providing the service. I also agree with an earlier poster - to try to imply that anything from Jolida or Primaluna is in the same league as VAC gear is just wrong, IMHO.
Put your favorite EL34's into a Cary SA 280 V12 with a good recording and some great matching speakers and you will hear and feel the piano as amazingly live in your room. This Cary will go from ultralinear to full triode in 1/3rd increments ( on the fly) and you'll find your sweetspot somewhere in there...It also does KT's and lots of other tubes too but for what you described, go with the EL 34's. Good luck and happy Lissn'n.