That's a waste of your time and mental energy.
The Alpine HU voltage is decent. They make good preamps. You can often hear the difference.
All the Alpine HU preouts are discrete, unlike a cheap EQ where the outputs are divided via a fader into front and rear.
Preout OP amps are not like high current amplifier outputs that keep increasing power as you lower the load by adding more terminations (speakers). You don't want to unnecessarily use 'Y' adapters to divide the preamp output, especially with a 2V unit, because the voltage to each amplifier input will drop. Instead, use a higher voltage line amp to facilitate the division.
The JL Audio amplifier has both a high voltage (lower sensitivity) and low voltage (higher sensitivity) input selection plus a variable sensitivity control. It's going to be hard to find a mismatch unless you start dividing RCAs without boosting the voltage.