Speakers like the Atrias are relatively tough impedance loads. As such, when paired with most tube amps, there is a mid-bass boost, hence the warmth. Actually, tube amps create this effect with the vast majority of speakers (why peeps claim tube watts sound more powerful), even many high sensitivity speakers if they don’t have a mostly resistive load.
You are probably experiencing a much more linear response with the D’Agostino. If you don’t have the luxury of experimenting with speaker placement, you can try reversing the speaker cable polarity. That may cause a bass boost or null depending on your room acoustics and the amp’s output polarity. Otherwise, if you haven’t had the amp for long, you might do well to give your ears more time to adjust to the new sound.
Chances are that upgrading to a “better” D’Agostino amp will not provide the missing “warmth.” Maybe consider a Sim Audio or Boulder integrated.