The Scarlett Solo should drive the 990s.
https://www.amazon.com/Focusrite-Scarlett-Audio-Interface-Tools/dp/B07QR6Z1JB?th=1
First question and answer:
"
can this power 250 ohm headphones?
Answer:
Hi,
As a general rule, we believe that the headphone output on the 3rd generation of Scarlett interfaces will supply enough volume to the listener when using headphones with impedances of up to 250 ohms. However, this is also dependant on a number of different factors and not just the power the output supplies - for example the sensitivity of the headphones you're intending to use, how loud each individual prefers to listen to music, and the effect of any background noise. There is more to the headphone specs than just the power output. We've tested the new design with a variety of different headphone models here, with a wide impedance range without issue. Unfortunately it's often difficult to say whether a particular headphone model is likely to work well with a particular headphone amp design without testing that combination first!
Best regards,
Laurence Clarke // Focusrite Technical Support"
If it can drive some 250ohm headphones the 990s are on the list as they aren't terribly hard to drive. Bright enough to make your ears bleed but not too hard to get loud.