DT1990 DAC/AMP Help

[mathiasd0e]

Hello,

I am quite dumb so I need your help. I have been using a MMX300 with a Sennheiser GSX 1000 for the last 2 or so years and have recently upgraded to a DT1990 Pro.
I am very happy with these headphones but I would like to get the most out of them. I mostly use them to listen to music, so I don't really need any of the GSX's features.
I have been looking everywhere for recommendations on what to buy, however I always end up having more new questions than finding answers.

My budget is around 300€. 
I was thinking about getting a Magni/Modi stack for a long time, however I see many people recommend the Asgard 3 here.
Would I get better sound if I buy just an Asgard and then invest in a DAC at a later time? What DAC should I get?? Can I use the GSX as a DAC or is it trash? 
Or should I just get the Magni/Modi stack? Are there other better options?

Pwease help ;-;