Old question, you’ve probably moved on. I’m just trying to clear up some older questions.
Anyway, I’m not going to go into all the details, but hopefully get other people looking to solve a similar question headed in the right direction.
In a case like this the first thing you need to do is edit the advanced search form to add the new fields that you want to use. Then next step would be finding where the query is run using these fields and alter that query to include you new fields and values. There really isn’t enough information available in the OP to go into more detail than this.
Hope that helps someone.
