If the amp is rated for, say, a 1V input and you gave it a 4V input, then there would be significant clipping of the signal as you turn up the volume. For best audio quality the full volume (0dB) output of the empeg should equate to the maximum amplification that you desire within your system, which means that the amp needs to be able to accept an input of about 4V.

Any half decent vendor should be able to tell you this characteristic, or check on the manufacturers web site.

Rob