If I might make a suggestion,
Get some D-class Estes rocket engines (any decent model shop will have them) and the igniter set. Seriously better thrust and you can ignite multiple engines simultaneously, ensuring that it's well the fuck away before it goes.
The problem with using more than one firework is that the fuses aren't always equal. We made a rocket with three fireworks attached to a cardboard tube with an egg on the top. The first two fired at the same time, raising it a foot or so before tilting over at which point the third fired and the fucker decided to come for us...
( Colonel Boris "...a desperate Buzzfeed imitation...", Wed 16 Mar 2011, 9:29, 1 reply)

Estes rocket motors don't explode, much
So I don't think it would fire the Mr Muscle up. Now, if you combined the pyro effects from the firework with the propulsion of the motors, you might have something...
(moon monkey is busy making memories worth repressing, Wed 16 Mar 2011, 9:38, closed)

I wondered about the ones with the parachute charges.
Given the speed the things go off at, what about mouting the rockets nearer the top of the can - then the weight of the can stabilises it and hopefully the flame eats into the can.
???
Profit?
( Colonel Boris "...a desperate Buzzfeed imitation...", Wed 16 Mar 2011, 9:50, closed)

Yes, they spout fire out the end to pop the parachute
but it's more a puff than a bang. Should be enough to light the pyro package, tho.

The can-behind-the-rocket design sounds unpredictable!

A D motor gives 20 N-sec impulse, or an average of 12N for a little under 2 seconds. The weight of the can is going to be around 2N at a guess. So you won't get much height. But we're not bothered about the pressurisation, so emptying out the can into capsules strapped around the pyro would work.

This is all of course hypothetical...
(moon monkey is busy making memories worth repressing, Wed 16 Mar 2011, 10:40, closed)