From what I've read, the GX76 has a dual mode but it doesn't work as expected. Here's what I found about dual mode:
"...negatives are: (a) you can not make the keyboard sound dual voices [BUT I can now 'cheat' this by connecting midi out to midi in - if u briefly disconnect at one end and change channel, keybd thereafter sounds both voices]; (b) split keybd only works wioth preset instruments; (c) as far as I knwo u cannot select individual midid channels."
It should work well in split mode based on what I've read so far.