maybe has something to do with matching gain to prevoltage rca. maybe the amp as made with 2v preouts in mind only... 4vpreouts are still good. ment for multiple amps or todays amps. I believe some amps can take from .02volts - 4 volts, 6 volts, 8 volts. from preout. basically means gains matching a litle more flexable. I am sure others will chime in here and expound on what I said.