The phrase "sit down with" means to have a conversation or discussion with someone in a relaxed setting. However, there are many other ways to express this idea using synonyms. Some examples include "convene with," "meet with," "discuss with," "talk to," "have a chat with," "consult with," "brainstorm with," "engage with," and "debate with." Each of these phrases carries a slightly different connotation and may be more appropriate for a particular situation or relationship. By increasing your vocabulary of synonyms, you can add depth and nuance to your conversations and better express your thoughts and ideas with others.