Well I don't want to encourage further upgrade-innitus so to speak, as I personally have no plans on going this way (not with the Euforia anyway), but here was my experience:
For a brief time at SoCal CanJam I tried the Meze Emypyrean headphones on the Euforia. I had to ask a vendor at another table to borrow them since they weren't at the table with F.A. amps and he was escorting me so it had to be a brief listen, maybe 2 min. at each of 3 amps. First off was the Euforia amp pairing, indeed sounded "fairly good". Mind you the Euforia itself was not up to full potential either using stock tubes and the only source was just a good DAP (forgot which model) via 3.5mm to RCA output. Definitely everything was 'there' and sounded right, and if that was the only thing around I could certainly have gotten used to the pairing and even become quite fond of it... but quite the opposite, myself being in a super CanJam filled to the max. with basically every current mid to top-tier flagship Headphone, DAC, amp - an audiophile's dream where we can experience first-hand what is really possible with sound reproduction without pre-condition or bias. So next up was the Prima Luma EVO 200 tube amp - though not their priciest model I was told that it's headphone output is on-par with their higher models which are more built to drive speakers. The difference with the PL 200 amp was immediately noticeable, taking me much deeper into the scene of the music... instead of 'observing' things in the recording you can actually 'taste' them - drums are real instead of simple being a good recording, to make an analogy, and a better performance with everything from instrument separation harder hitting dynamics, etc. These headphones scale well and these types of incrimental improvents are obvious when climbing up to higher amps. Next I tried them with the Quad PA One + amp (using internal DAC) which to me was quite unique: dynamics were possibly just as hard hitting as with the PL 200 amp costing almost 3x more and with a more vivid sound but not quite as detailed and a slower decay to the drums. To me this pairing may have been better than the Euforia in some ways, seeming like this amp has much more sheer power for a more dynamic / weighty experience but I do suppose the scale could tip either way with the Empyreans on the Euforia or the Quad PA One depending on source, tubes, etc.
I also tried the Empyreans with other amps such as WA33 and it came really close to being a showstopper, but as mentioned with the endless array of super hi-fi gems being at a Can Jam, even with cutting edge protoypes on hand I can tell you this with certianty: The Empyreans sounded better on the WA33 than former amps (more resolving, more of everything), however this experience is faint in my memory compared with: The new planar Headphones Rad-0 from Rosson Audio on the GSX-mini solid state amp drivin by Qutest + Mscaler which was bested by the Rangarok 2 amp + Yggdrasil 2 DAC with this headphone, which was also bested by what I currently with no reservations whatsoever consider the all-time current king: the divine, the sensational new breakthrough in "electrodynamic" technology known as HEDDphone One made by a German company who are making a solid entry into headphone production after 30 years of making speakers used in studios. This headphone blew me away even on mid-fi amps I tried it with such as the Quad PA One and especially with the PL 200 amp. A sound that's hard to put into words, just look at my post in recent pages here to my review of it. However as a Euforia owner I'm not recommending any of these as an "upgrade" path. The Rosson Audio Rad-0 did not have 'synergy' with the Euforia and the HEDDphone One was simply not driven loud enough even with the volume up all the way. Of these the most comparable is the Rad-0 to the Empyreans, as these are both planars of around the same general cost. I preferred the Rad-0 to the Emypryeans for a more 'coherent' sound somewhat more vivid, lush and engaging but certainly the Empyreans are resolving and do basically everything right and are by no means in-coherent, but my contrast the others had a more refined and modestly more laid back sound. These would rather be a side-grade than an upgrade if any at all since you would need to also replace to an amp with more raw juice to properly drive them.