Hermann,
Thanks a lot - that's already quite helpful.
RSDS_RANGE_TO_WHERE happens to have the restriction that the fieldnames must be valid as names of components of an ABAP structure, e.g. generating WHERE clauses such as
T1.PARTNER = ... AND
T2.STREET = ...
won't work - but it's easy to use for WHERE clauses where field names do not need to be disambiguated with respect to their tables.
FREE_SELECTIONS_RANGE_2_WHERE is a bit less comfortable to use but makes up with greater flexibility.
Thanks a lot! 
Best,
Thorsten