So, in general, no -- there is only one split point for tones or voices, and you can have main and dual voices on the right side of that split point, and the split voice on the left side of it.
With that said, there may be a few tricks that can be employed that might give the effect of additional sounds or zones. Some of the keyboard's sounds have a significantly different tone -- especially when played forcefully (with key velocity switched on) -- on the lowest notes compared to the notes an octave or so up. Using a tone like this on the split voice helps give you more tonal variety because of the difference in timbre between the lowest notes and the slightly higher notes, so it is sort of like splitting the left side of a split keyboard when you use a tone like this. But of course, you're quite limited as to the selection of sounds you have -- you cannot simply select, say, a bass guitar on the left, strings in the middle, and a piano on the right. But you can experiment with different sounds to see which ones have the wider variety of tone/timbre in the lower two octaves or so. And experiment with different octave settings for the split voice as well, to see which setting may have more of an effect.
Another possibility is that, with the right software and procedures, it might be possible to set the auto accompaniment split point and split voice split point to two separate notes. I remember this was possible on older versions of these keyboards (not sure if it would work on the newer models), but you could not do it on the front panel -- and I never personally tried this -- I just read about it here. It seems there were two separate registers or numerical memory locations internally -- one for the split point of auto accompaniment, and one for split point of the split voice tone. The controls of the keyboard set both values together and keep them equal. But someone very knowledgeable who used to be on this board (Michael, userID SeaGtGruff -- apparently hasn't been logged on the site for over a year) found a way to, I believe, take a USR file (basically a memory dump of all of the keyboard settings onto a flash drive), load that file from the flash drive into a computer, then read the data with a hexadecimal data editor, or hex editor. If you know what you're doing at that point (and I don't), you can find those two memory/registers (the one for auto accompaniment, and the one for split voice tone), and then set them to different values. You could then save the edited file back to the flash drive, the load the file back into the keyboard, and then the keyboard would now have those different split points for auto accompaniment and split voice tone. I believe these memory/registers were actually part of the registration data, so that when you edit the USR file, you're actually editing the data for a particular registration, and then when you bring the USR file back to the keyboard, you have to select that particular registration to get the the updated values for split points for auto accompaniment and split voice tone. These updated values would stay in effect until you either changed the split point again by the control panel, or selected another registration.
So, what did all of this do? It allowed the lowest part of the keyboard to be set for auto accompaniment (which would also be combined with the split voice, as that is simply how the keyboard works when the split voice and auto accompaniment are both switched on), then the middle part of the keyboard (above the auto accompaniment but below the split voice tone split point) would be the split voice only, and then the notes above that split point would be the main and dual voices.
Of course, you have to be very careful when editing USR file data and then putting the modified USR file back in the keyboard, because if it isn't done correctly, you could mess things up. And I'm not sure if this would still work on the newer keyboards like the PSR-E453, PSR-E463, and PSR-E473 or not.
