Higher signal from BOSS IR-2?

Long time first time.

tldr - how do I get a higher volume (signal) out of the headphone jack of an BOSS IR-2?

So I've been learning pedal steel at home with a 2-year old, the BOSS IR-2 with headphones has been a revelation. The instrument really thrives on a clean-ish tone, I've upgraded the IRs for both the twin reverb and vox ac-30 from York and they're excellent.

But my issue is that to get the tone I want i need to keep the GAIN below ~25%. But to learn the instrument properly (specifically using the volume/expression pedal, which you pick at, let's say, 70% volume) I need more signal. I'm using these headphones (just an arbitrary pickup like five years ago). I have the volume all the way up and it's not loud enough (again I could jack up the GAIN but then I'm not hearing what I wan tone-wise).

Is this something I can "fix" with different headphones, or should I get some kind of in-line booster? How do I pick one if so?

Thank you.