Forget Super Bowl rings, Peyton and Eli Manning are chasing Tony Awards now ... 'cause the two NFL legends dropped a hilarious "musical" in honor of their hit "Manningcast" show -- and the cast is chock-full of big names!!

The quarterback bros showed off their singing chops in the 10-minute promo for their upcoming Omaha Productions' "Monday Night Football" broadcast season (they've won Sports Emmy's each year) ... but they weren't alone on stage -- enlisting football faces like coaches Andy Reid, John and Jim Harbaugh, Mike McDaniel and Brian Daboll to get in on the magic.

There were a number of players sprinkled into the clip as well ... including Myles Garrett, Baker Mayfield, Gardner Minshew and Ja'Marr Chase.

While the performance was purposefully silly, there were also some actual GOOD crooners involved -- Michael Bublé and Ravens kicker Justin Tucker, who's a trained opera singer.

The whole video is stuffed with cameos from non-NFL figures, too ... including Pete Davidson, Kevin Hart, Livvy Dunne, Druski and Snoop Dogg -- who did a special track about quarter-zip sweaters (a Manning wardrobe staple on the show).

In fact, the Mannings got commish Roger Goodell and legendary coach Bill Belichick to participate in the project ... so they really pulled out all the stops to bring it all together.