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For that keyboard, the three presets that are marked as 'Strings' more or less, are under the
Preset C bank (PR-C):
035 St. Strings
036 Warm Strings
037 Somber Strings
040 String Ens
061 Deep Strings
and a few other less likely-sounding ones.
Do you know how to bring up the Preset C Bank? if not, I will give you instructions.
PS: Also, the
Try accessing expansion banks via the shift key: Shift-7 is supposed to bring up Bank C.