I have the yamaha PSR8000 (still) You dont have to lose the arranger function by playing the bass in the left hand. A compromise is to mute the accomaniment bass, split the keyboard and transpose the left hand side of the split down an octave or so. Select a basss sound for the left hand .You can alter the way that the accomaniment follows the chords you play so that it triggers on the chord that you are playing. It takes a little experimenting to find the setting that suits you best but i have found i am able to play nice funky bass patterns with my left hand and chords with the right and still maintain the arranger function.

Another trick that i discovered only recentley when considering upgrading to the PAX1