Is there a way to increase the volume of the guitar through the guitar line input? I have everything all the way up but it's still too low on new DP004.
I don't have mine in front of me at the moment, but you should be able to adjust the input gain via one of the buttons on the top, towards the back of the unit. I think it's called "Input setting", below the Power button, I think. Anyway, you should be able to get into the mic/input menu and adjust the "guitar/line" in in three stages; low, medium, and high. It should be covered in your manual though. You just have to play with it a little bit to make sure you aren't overloading it after changing the setting.
If you don't have the ability to change the low, medium, and high settings on the "Guitar/Line", you need to perform a firmware update on it as that is what introduced that feature. Hope this helps a bit.