Add to a group of ideas. The phrase implies that a topic is being discussed or investigated and someone wishes to consider another factor that may have an impact.  ‘Mix’ in this case refers to a line of thinking or a list of items and you want to add something, new or different.  To ‘throw in’ means it may or may not be of importance. (Compare to Add my two cents.)

“At work we had a long meeting about who would buy our new product and I said I’d like to throw into the mix my investigation of  buying habits of teenagers.”