Steam mussels before or after adding other ingredients?

Hello guys, I'm making a mussel dish and have everything in order. The only thing I have been wondering about is whether it is better to steam the mussels before adding the onion, garlic etc, or to saute the garlic and onion then add the mussels to steam. The recipe im doing says to just coat the pan with er then add them and steam for 1-2 minutes, then add in garlic, onions, tomatoe and alcohol(anisette) and to cook down a bit. But steaming them before adding the other ingredients seems like it would make them lose out on some of the flavor, so I was wondering how you guys prepare them, steam first or saute veggies then steam.