I may have the "heat spectrum" covered, however, since I use the Aries/Gungnir with a Freya pre-amp and the pre-amp (JFET or tube output) into either a Class A (First Watt F7), Class AB (Hegel H200) or Class D (Taranis) amp. Speakers are Totem Forests or Silverline Prelude Plus, depending. The F7 and Hegel seem warm to me. The Taranis less so. The Preludes definitely convey more treble energy than the Forests, though the Forests have metal dome tweeters.
Very happy with the results from all the various combinations. None or muddy and slow due to an overly warm presentation. None are ear-bleed bright. FWIW - I do freely admit to tweaking the various combinations with different tubes, cables, and positioning.
Hope this is at least somewhat relevant to your inquiry.