Ya the problem is the 250 Ohm version of the headphones require too much power than your device can give it!  That’s why it’s not very loud.

If you’re within your return period, I’d say get the 80 Ohm versions to make the most of your money at the moment.

If you look at the “Tech Specs”, your audio interface says “60 mW/Ch @ 60Ω Load” which seems for a lot of “consumer” type headphones.  (Even the new version of it has the same specs!)

I’m not able to help you too much for the headphone stuff, as I don’t know the technical stuff of impedance etc.

My audio interface at the moment is wall-powered + usb connected, so I get TONS of gain for my needs (almost too much!)

Sorry I can’t be of more help here, but the issue is the 250 Ohm headphones.  If you can get 80 Ohm or lower, you’ll hear your audio much louder!