Kana,
That's a good question. The difficulty of finding *any* suitable higher power pentode or tetrode push-pull amp using modern tubes and having natural voicing is enough to make my first recommendation abandonment of lower-efficiency speakers. But I know not everyone will do that. It would send a hell of a message though. If I needed ~75w/ch and I was predisposed to tube amps to get it, my first stop would be the Melody 845 push-pull triode amp at 70w per monoblock. Cost is similar or less.
Another option available to you because of ARC's long history of owner-friendly business policies is to find a good condition ARC Dual 76A and send it back to Minnesota to be refurbed to current standard, and then have a local tech retube it again with known NOS tubes.
Another option is the Tim DeParavicini-designed Quad II-Eighty monoblocks. Also his EAR Yoshino 899 or 890 power amps. As someone mentioned, big VTLs in triode mode are contenders. That's a flash answer to your question. If I think of others, I'll circle back. I mostly find natural sound between 5 - 50w these days.
There's also always McIntosh, though I think in powerful amps their quad-differential/autoformer output SS models (specifically and exclusively) are now preferable to their push-pull tube amps -- which is an exception for me to say. They're not a clear preference over ARC REF -- just different. In some respects these are all "lower-tech" circuits than the ARC REF amps, but for convincing musicality at the 75w power level from tubes, they are honest alternatives I hear as more natural, sonically. But they are also all amp types that are in my rear-view mirror.
Phil