Hi Todd,
The "Guitar & Amp" button you mentioned on the "Mic/Guitar Setting" screen is not specifically explained in the PSR-S970 owner's or reference manuals. It takes a lot of patience to dig out what it does.
Let me walk you through the experiment I did on my PSR-S970 with screen captures to illustrate how this "Guitar with Amp" button works.
When you first press the "Mic Setting / Vocal Harmony" button, the default setup is:
Mic/Guitar ON,
Effect Type (DSP4) Assign Part: LEFT Type: Ensemble Detune 2
You can then press the "Effect Type (DSP4)" button to the "Effect" tab of the "Mixing Console" to select your choices of:
Block
Assign Part
Category
Type
Then press "Exit" button, your will be presented the "Effect" tab of "Mixing Console (Panel)" where you can do more tweaking:
Then press "Exit" button to return back to the "Mic/Guitar Setting" screen and save the changed "Effect Type (DSP4)" to Type "User1". Suppose now you switch the Mic/Guitar switch at the back of the PSR-S970 to Mic, and press the "Talk" button to talk during your performance / gig, you notice that the "Talk" button on screen is lit up, with no change of "Effect Type (DSP4)" - still at Type "User1":
After you finish talking, you press the "Talk" button on screen to turn off "Talk" and the "Talk" on screen button becomes unlit / grayed out, and slide the Mic/Guitar swtich at the back of the PSR-S970 back to Guitar position, you will notice that the "Effect Type (DSP4)" setting remains at Type "User1":
If you press the mysterious "Guitar & Amp" button, the "Effect Type (DSP4)" setting is changed to:
Assign Part: Mic/Guitar
Type: Multi FX Distortion Basic
Now you can see that this undocumented "Guitar & Amp" button actually works - to change the "Effect Type (DSP4)" to:
Assign Part Mic/Guitar
Type Multi TX Distortion Basic
Thanks,
Paul