My experience is that if you use a Nucleus or Nucleus+ as server & player, it tends to be mediocre. Just as a server (which I assume is what you are doing with Mola Mola), it performs at a very high level. The issue is the processor is too powerful to serve as a good player.
Where I find there is significant improvement is if you introduce a master clock like what you see from Antipodes or clocking between server and DAC can be synchronized. This happens with I2S connections or when there is a dedicated clock connection.
My most common upgrade in servers is customers who go from a Roon Nucleus or Nucleus + to an Antipodes K50.
You are on the right track with Aries Cerat or Lampizator. Both are very, very good though I tend to like Aries Cerat better. Personal taste though.
The obvious other two options to me are the MSB Premier and the Playback Designs MPD-8 Dream DAC. There is a slight sweetness to both with a complete lack of brightness/sibilance that is quite shocking and enjoyable.
Theoretically, those four units should do the job and will all be a touch warmer than the Mola Mola while delivering the same of better levels of detail.