It's 2V unbalanced and 4V balanced. My SD transporter puts out 2V unbalanced and 3V balanced. I never really had a problem with the input. I bought a c2300 preamp and hooked it up. I could turn the volume up loud enough to start seeing the power-limiting lights kick in but it never seemed to really get much louder than without the preamp. My speakers are inefficient (86 dB) so they can pretty much absorb all the 402 can throw at them. I decided I didn't need the pre-amp after all. The DAC at full volume is more than loud enough and I never listen to it all the way up. Even at -5 to -10 dB it's really too loud to the point that it makes my head and neck tense up. I wouldn't necessarily worry about getting that last volt or two out of the preamp. In my experience it's unnecessary.
