I like the response or Bruno ROCCA... treat the PM like a SPOUSE... Yes, I capitalize because it is that important.
As a founder and the "former PM" I salute the idea that you can go into any meeting you wish, into anyone's office you wish, whenever you wish. However, discretion is crucial in order to build confidence and TRUST with your team.
Attend the Project meetings... take notes, observe, comprehend... but, let the PM run the meeting / the project and program. Your comments, counsel, advice, questions, and redirection should be done IN PRIVATE. Allow the PM to lead and grow and gain the respect of the organization.
You may be dynamic as a founder, visionary and industry leader. However, building an organization for the long-term requires a different skill set... step back, watch, lead in a different way.
I have LIVED this in dramatic fashion with one of the most Iconic Founders and Visionaries of the past 50 years - Michael Dell. Michael would attend my meetings, walk into my office unannounced to discuss strategies and particulars, and would show confidence and trust in me and my team to execute. Michael has a reputation as tough and demanding - so what. Michael always allowed those that had their act together to lead. Michael would walk into my office unplanned and unannounced to discuss details, issues, strategies, and plans. 99% of the time he just wanted to know what I was recommending so that he could support the strategy.
Be an Iconic Founder and Leader. Guide, protect, build, support, and grow!!!
Enjoy being a founder of a growing organization.