Splitting the signal from the dac

Why not use the additional output from the preamp, assuming you are feeding into one?: DAC into preamp, and send the various pre outputs (you can get an RCA splitter if you only have a single output) to your various amps. In that case there would be no problem at all.

Not quite the same since we are concerned with voltage, not power, here. The answer depends on the output impedance of the DAC and the input impedances of the two loads.

Kal