I would be more worried about the imbalance on the sequential flux capacitors. That is is a really difficult phase correction to fix after installation.Splitting the RCA signal with a Y cable does NOT cut the voltage in half. The input impedance of those amps is so high that they are very little load on the preout drivers. I wouldn't bother with a line driver unless you can't get the amps to full power without it, but I sincerely doubt you'll have any problems.