DT990s and a GoXLR, how do I increase volume?

[cHk4]

I got the 250ohm DT990s and for the most part volume is pretty good with the GoXLR's phantom amp but I want something to boost it a tad more. My understanding is I need an AMP but I can't use a DAC/AMP combo? If so what's a good AMP to get to connect between my headphones and GoXLR? The budget would be sub £200.

Thanks