Driving a poweramp

[bongomania]

I need a DI with an additional line-level output.

Fixed it for you. Big +1 to everything greenboy said there, particularly the bit about "channel strips" as opposed to standalone bass preamps. You're much more likely to get an un-EQ'ed, un-colored, un-"preshaped" signal from a decent channel strip.

 

[A9X]

Just to be clear to the OP, what you are asking for is a preamp. You're absolutely right that most basses do not put out the right output to drive a power amp, and that is why amp heads contain preamps, and why power-amp users use preamps. That gain boost is, at essence, the definition of a preamp. So if you want the cleanest signal, it's not that you don't want a preamp, it's that you want the most transparent preamp you can afford.

All true, and also for the OP, most passive basses will be expecting to see a load >500k ohm and most poweramps are <50k ohm. This will load down the bass, reducing the signal level and remove a couple of octaves off the high end at best. Most poweramps are balanced input, and may or may not ba happy with an unbalanced input from a typical bass.