Does anybody know what is the best way to tweak the equalizer for avic x 930 bt in order to get the best possible sound?

if not by using some appropriate "reference" material and good "ears" then maybe an easy way like using auto-eq feature (requires eq mic accessory)

Try these: 3, max, 3, 2, 4, 4, max, 5. You can smooth out the treble if drums/cymbols are too harsh by decreasing the last setting.