Hi Jun
You should be able to adjust the output of the ES-8 up 4 semitones in the Silent Way plugin? Have you tried using the Detune-->Transpose or Override-->Pitch controls?
Even adjusting the voltage tables will not fix the transposed note display issue that you are having because the mapping between voltage and displayed note is fixed (C0 is 0V, C1 is 1V and so on). I can put such a configuration option on the TODO list (it would be CONFIG.INI based) but it will be at least a month before I can get to it.
Either way, please let me know if you were able to fix the display issue from within Silent Way.