how to win against this very defensive formation

[Potemy]

Considering your side is better on average quality, I'll assume your players beat his man for man.

----------ST----------
AML-----AMC-----AMR
-----MC--MC--MC-----
-----------------------
-----DC--DC--DC------

This is my suggestion as I prefer to play variations of 3-6-1. Your 3 DCs should be able to deal with his 3 STs. You say you have no DM and M wings, so I've placed flankers for you on AM. Other than that, you're free to adjust the other 5 players, maybe you'd like to play with 2 strikers instead, but I would not place them any further back, he doesn't really have much in the way of attackers.

Red arrows on all AMs, MCs will cover them, and no arrows on your ST or DCs, short passing.