I have been tweaking the tone breaks and audio tones in DI4 mode yesterday. Here are the settings that are working well for me so far.
Basic Menu
Gain=90
Disc=0
FeVol.=3
Expert Menu
Notch=0
Audio Tones= Fe=15, Gold/Non Fe=40, Non Fe=60 and the last un-boxed=70
Tone breaks= Fe=20, Gold/ Non Fe=68, Non Fe=80
This has been working good and gives a nice rollover audio effect on mixed metals so far. I haven't decided how low to go on the Fe tone break because I have only dug foil balls in the 20's range. I set the Gold/Non Fe at 68 so it gives a 2 tone rollover sound at a Zinc penny. I'm also not sure on the tone break for the Non Fe yet but these settings put everything above Iron into an audio zone, copper into another and silver into another. Please adjust the tones and breaks to your liking. I usually use zero disc in the Settings menu and use the Notch feature in the Expert menu to adjust how much iron I want to hear. This keeps the machine running at its highest sensitivity.