How do i specify an AND via soap for SET datatype, by default it seems to be an OR?
While it's not possible with the infield: syntax, you can define a custom Parametric Search Query that uses the field twice.
$qpField1 IN setField AND $qpField2 IN setField
Now you can use multiple <Param> elements to set qpField1 and qpField2, and it will only return rows that have them both in setField.