I'm an EL-34 fan myself, and own an EL-34 only amp, and I would say check out the Gold Lion KT-77 this EL-34 variant to me was a huge upgrade in my amp over the likes of JJ, EH, etc. A very worthwhile upgrade and inexpensive as tubes go. This will likely give you a bit warmer sound than the KT-88 though I haven't heard your amp specifically.
Primaluna Prologue 4 tube upgrades
I recently acquired this amp and at first thought it was sounded great, but was not completely happy with the LF response with my modest Dali Zensor 1 monitor speakers and nicely upgraded Dared SL2000a amp. So, I swapped some Siemens 12AX7 and 12AU7 tubes into the unit for the stock Chinese tubes and holy hell, this amps is really quite fine! It has great control of the LF now and I realize that a veil of grunge I was hearing has vanished! I might swap some better power tubes in for the stock PL (Chinese) EL34's to see if that improves it even more. Or roll some Gold Lion KT88's into it. The amp has the unique feature of auto-biasing the tubes, which was always a hassle with my HK Citation I and V amps . Honestly, I have been thinking about upgrading to PL's high end integrated amp, but from what I hearing today, I might just stay with this set up. BTW, I have had a long series of far more expensive monitors in my system, yet these Dali Zensor 1's are the best I have had. They are thoroughly musical.