actually, i think that behringer unit is looking for a line level (not instrument level). so in this scenario you'd plug into your head, and then take a line out from the head and plug into the headphone amp. there are more simple solutions. what exactly do you want to do? you mentioned recording, and practicing at night. i use one of these
[Invalid or Expired Link Removed] which you plug your bass into (has a preamp) and plug in my headphones (has a headphone amp) ... it also has another input for playing along w/ recordings or whatever, and separate volume controls to mix your bass and the other input.