I never worked with IT, but got a few unfinished IT-modules from a friend of mine to work on, but they sound “strange” when I load them … did any IT-user recognize flaws in the IT-import feature or is it just the way my friend makes his music ?

There is a whole host of problems with it. Any IT (MPT) module of mine is pretty much unlistenable in Renoise as of now. The biggest problems would seem to be the instrument envelopes (they don’t load right, they usually get a length of 6), samples (Renoise sets up loops where there should be no loops) and multisample instruments (Renoise can’t handle instruments with more than 16 samples, and when you load a song with such an instrument the results will be … colourful).