I believe the channel balance setting doesn’t work in DAC mode. If you set the E70 to preamp mode and adjust the balance from there, you are not going to lose any appreciable dynamic range. Putting the E70 in DAC mode only fixes the output to maximum level. That ensures max dynamic range, but the E70’s dynamic range is already a good bit higher than the threshold of human hearing. You won’t lose any fidelity by using the DAC in preamp mode at max output and attenuating volume with your downstream preamp.
The E70V is an incredibly good DAC. It can embarrass many a four-figure DAC.