Mouthpieces to play on a 10 members marching band

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I have some friends playing on a mini marching band (10 members).
They asked me to buy a mouthpieces to have volume. The problem is that they play with a very closed mpc, like Selmer C** or D.

The only mpc that I can recomend is the vandoren jumbo java with the lowest tip oppening for altos and tenors, and maybe the runyon custom spoiler for soprano.

Any suggestions for my friends?

Thanks.