Okay, I think I understand what you're trying to do...
You can select a voice from the keytar, but it always uses that voice's preset voice settings (reverb type, reverb depth, chorus type, chorus depth, channel volume, pan, octave, attack time, release time, filter cutoff, filter resonance, etc.).
What you want to be able to do is either recall a user voice from the keytar, or a registration, or otherwise select a voice that has the settings you've chosen for it, rather than being limited to just the preset voices.
I'd have to look over the manuals for the AX-7 and the PSR-S970 to see what's possible.