Ditch the line driver, the deck 4v is plenty. The power difference is zero, the amps rail voltage doesn't change. The advantage is with the deck's voltage, there is more dynamic range in 0-4v than 0-2v. The amps gain will boost the signal to the rail voltage either way. If anything it will likely "color" the music, I've played with quite a few op amps and they all sound different.
99 s10 Blazer 2 door 5.7L Vortec swap
4- Team Ascendant Audio 18's
4- Ampere 8.0 TFE's
2- Zed Leviathan's
20 banks Maxwell caps
Team Ampere - Team Heavy Flex +160dB