Hi,
In this case I’m afraid the drop-down selector is not possible, because buddyPress xprofile fields are not user meta fields (custom fields), so those cannot be used as filter criteria.
I have cleaned up a bit the buddypress xprofile section, so that only the fields are selected, as for some reason the values were there as well.
You can also enable the secondary logic, if you want to – so that you might get better results when multiple keywords are entered from different fields.