I am pretty sure it would still be 4V to both. A splitter should just split the signal, which would mean the two amps are in parallel to the empeg. Therefore they would both still get the full voltage of 4V, just less current. Since the current doesnt really matter as the amp is not really drawing current, there should not really be too much effect. As far as having both your fronts and rears on one output, you can still control how much power goes to each (fade), but now you have to do it with your amp's gain instead of with the empeg.