Try a different tube amp.
Watts don't mean squat. It's all about build quality. At one point, I had 250-watt solid-state monoblocks with 95 dB speakers. Now I have an 8-watt tube amp and it is far more dynamic than those monos could ever dream of and much more refined.
Just curious. Are you using a 300B amp on Spatials that you own or are you using another brand of speaker?
I have owned many tube amps: from .75 watts to 40 watts. 71A, 45, 2A3, El84 300B, 6550 etc. Once you get much past 20 watts you are moving into "space heater" territory, with multiple output devices per channel. I have owned a couple of 300B amps. It seems that unless you spend a LOT of money ("build quality") you will get a magical midrange but with tapered off extremes ...even if you do get good dynamics.
My only point was that one might also consider wattage when powering Spatial speakers. I cannot make a recommendation for other speakers but I could see benefit with my X5s in at least that one category. The speakers have always seemed refined with spooky clarity but I had never felt them as powerful before now.