I would address those speakers, and leave the other components for now. Replace the speakers with a pair of used Klipsch Forte II's or Chorus II's and I'll bet you'll be cooking with gas for the kind of music you like. Those speakers do very well with tubes. Before taking that step I'd really make sure that there wasn't something wrong with the gear you already have. I've not heard anything with the "new" Mullard EL-34, but the NOS ones certainly are of the very best out there. Does your amp require manual biasing, and if so, have you checked the bias? Have you checked all the tubes with a tube tester to see if they're good? Are any more than a couple of years old? I have no idea who did your upgrade, but the Dynaco's are certainly decent amps that wouldn't fall that short in the midrange as you describe. What about the preamp tubes - have you checked those and could any be getting long in the tooth? Also, what is your source component...you mentioned a Dynaco Tuner, do you also listen to CD and or LP? Do all sources sound flat in the midrange? The success of a system is a matter of synergy between all the components as well as their links, including the room they're making music in. The weakest will cause the rest to suffer. It could be your room too, but first check on the components and making sure everything is as it should be.
Marco
Marco