I don't have a triton extreme but I did extensively test a triton before buying my Kurzweil K 2600S (is about 5 years ago)
The reason I did not buy the Triton(allthough the triton had much more ready to go sounds) were;
1. No good analogue outputs (very noisy)
2. No good piano's (they might be improved in the Triton extreme though)
Since you did not buy the triton apparantly from your post, you might have a look at the kurzweil which also has the possibility of loading samples if you buy the board with the sampling option.
balanced outputs
highly editable etc..
To answer your question; (a kind of workaround)
If you can split the triton in 4 sections (which I don't know if that is possible) just select the same piano rom in all sections and record each section on different midichannels.
In the midisequencer you can easily pan the recorded tracks.
For ready to go piano sound with a proper balance I would audition other boards before deciding on a triton IF the piano is very important to you!
This is my personal opinion only so others might have complete different opinions.
Fred
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Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76