I thought I was having this problem, too, but then I discovered there are 3 levels of volume adjustment when you're using headphones:
- The individual channel levels
- The Master Earmix output level
- The Headphone level
I was using both headphones and earbuds (at different times), and couldn't get satisfactory levels on either of them, even with the individual channels up pretty high and the headphone level maxed out. Then I noticed the "Select" button for the Master and punched it. I had that level down way low, and turning it up made it plenty loud, even for earbuds. Problem solved.