I have owned the Sonic Frontiers Line 1, and in my opinion I find it to be quite neutral and not warm-sounding. In fact, the sound was rather flat across the spectrum. Tubes used were Sovteks and Amperex.
If you want a warm sound, I would suggest that you look elsewhere other than Sonic Frontiers and ARC, which I currently own.
If you want a warm sound, I would suggest that you look elsewhere other than Sonic Frontiers and ARC, which I currently own.