Increase Output Volume

Hi there. I have a slight problem that when I use the TRS outputs directly into my speakers (M-Audio AV40), the sound isn't loud enough and gets drowned out by my guitar or piano.

If I use the headphone output and send it to the speakers, the volume is fine. I don't like to use a headphone output as they're prone to crackly sound at loud volumes.

Is there anything I can do to boost the volume via the TRS outputs? I know I can turn up the mic gain, but I don't want to introduce clipping.

Cheers,
Trev