I hope you mean the Paris Museum Pass, which can be a good value, and not the Paris Pass, which most here feel is a big rip off. Be aware of the recent changes to the Museum Pass that now only allow one entry to a museum (so, for example, multiple entries into the Louvre during those 6 days is no longer possible). Also, the Louvre is also currently requiring advance reserved timed entry, due to crowding. You don't say how far away your trip is. If you're only doing 1-2 museums per day, I'd just pay as you go on the rest of your trip. Surely you won't be doing museums every day?
What will you be using for transportation? Given the length of your stay, the Navigo Decouverte pass (good for a week from Monday to the following Sunday night) might be the most economical, since it is good on bus, metro and RER in zones 1-5. You can renew the pass at the end of the first week for use on the next. A photo is required. Details are on the ratp website. You could supplement these with a carnet of tickets (bus/metro only, inside Paris) for the days not covered by the pass.
What day trips are you interested in? Trips to Versailles or Fontainebleu are covered by the Decouverte pass, and the Museum Pass. But day trips further afield will require train tickets.