Hi, it is fairly unlikely that your Marantz is causing the 'warm' sound you hear. Changing your amplifier is unlikely to give you much, if any, improvement in sound - unless you hear noise, distortion or you just need much more volume.
Change if you just want a change, but otherwise take a look at your speakers and their positioning in your room which is much more likely to be the issue. Dali recommend that you do not toe-in their speakers (face them straight ahead, not angled in to you) but that is something worth experimenting with. The same goes for distance of the speakers from any walls.
Your WiiM Mini has a Room Correction feature (RoomFit) which is much improved recently. Have you tried this? If you make some measurements using the WiiM and post them here then we can take a look.
Try these things before you spend money on an Amp, which may not help you