Working Audio Engineer here. There are three functional ranges of signal:
- Mic Level - This is the miniscule signal that comes from a microphone. It’s tiny! That’s why microphones are run into preamps. The preamps job is the amplify the signal to:
- Line Level - This is the regular, useable, routable signal bouncing around a mixer, compressor, EQ, ADC, etc etc etc, including your DAC. It’s strong enough to power headphones, but you aren’t really gonna move speakers with it. That’s why you feed your line level signal to a speaker amplifier so you get:
- Speaker Level - This is when you’ve got serious juice and could do some damage if you aren’t careful. Whether it’s 20W, 200W, or 2000W, you’ve gotta make sure you are sending the right level to the right gear or you can blow things up.
So... No, you don’t need a preamp. Your DAC is already outputting a Line Level signal, which is exactly what your speaker amp expects. Why add more gear, more noise, more devices to the signal? Could it help - maybe. Could it hurt - definitely. Sound reinforcement systems don't have pre-speaker-amp "preamps" as a concept even.
(In case anyone is wondering, my at home rig at the moment is a Peachtree Audio Nova125, which has an integrated USB DAC. It's the only unit between the computer and the speakers.)