Diana TC is one of the best headphones in the world. It definitely belongs among the top of the line (TOTL) headphones. It has TOTL clarity and speed, one of the best resolution of any headphone, amazing highs, and powerful, impactful, broad, yet tight bass.

You need a reasonable amp to drive these tho. Since you are describing them as quiet and not having much bass, it's certain you are not giving them enough power. These actually have one of the most powerful bass among TOTL headphones, definitely more than LCD5, Susvara, or Focal Utopia, for example. Even compared to one of the best, most punchy dynamics, the Focal Clear, the Diana TC's bass is vastly superior, sounding more like a top-quality sub.

For driving the Diana TC: On the more analytical end, I would recommend the Topping A90 or A90 discrete. If you prefer warmer, I would recommend the Burson Soloist 3x. Of course you can go up to Ferrum Oor or other more expensive amps if that's what you want as well. The Diana TC has amazing clarity and highs that beautifully reproduce the sounds of string instruments or sibilance in female vocals. Some people may find these annoying - the Burson, being warmer, definitely damps those down a bit, and adds to even a stronger bass. However be warned, since the Diana TC has very strong bass to begin with, adding even greater percussive pressure could be a negative - it's really all a matter of personal taste.