I've checked the manual and have to confirm that there seems to be no way to adjust volume of dual and split voices, just as the review stated. I imagine what a bummer that will be for future users and what an impression it will form for them of Casio's approach. No such surprises with PSR-E363, which costs about the same. It is like if Casio is careless on purpose, or perhaps this is how companies like Yamaha hold their positions - they make fewer mistakes.