Don't forget, you can set up the arranger of your choice to do Drums only, set up a LH Bass/RH comp split and do pretty much what you are doing, with the advantage that you have several patterns and fills at you fingers (or, even better, your feet!). This is how I do a lot of my gigging.
Perhaps the 88 wood keys of the QS8 is what you miss?
I would recommend you take a listen to Roland's G70, or E-series, others would say the Yamaha's, but all of the middle-to-top-of-the-line arrangers will let you do a LH Bass split, so you can continue with how you do things now while you get used to the LH chord system, or try Pianomode (just play pianistically, and it will figure out what to do!)
If you are going to work with SMFs, take a hard look at the Roland Makeup Tools SMF editing system - by FAR the easiest way to tweak SMFs (and styles) to your taste......
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An arranger is just a tool. What matters is what you build with it..!