What you are looking for doesn’t exist, at least not at 75 watts. When you start pushing tubes beyond 50 Watts or so they get much more solid state sounding (less second order harmonics). You’ll lose that single ended lush sound, especially with a neutral speaker like the Buchardts. Big horns and a SET amp will do it. Cornwalls, La Scala, Altec A5 etc. get big speakers for a big room and pair with a 300b SET amp. Twittering Machines has a video on YouTube with the Cornwalls paired to an 8 watt 300b integrated in a 35’x40’ room. Pretty impressive.
If you insist on keeping the Buchardts, try pairing with a monster class A SS amp. Something like a vintage Krell to keep costs reasonable.