I've tried it without the center and it did sound great, did not realize I was missing anything until I put a center in the mix. Center is a definite for serious HT. Not nessary if your not a big ht head. But the question I believe you asked was if you don't add a center will your pre still play 5.1 or in your case 4.1.. I will say yes to this, you should have the option of selecting a center speaker in the pre setup screen.
good luck..
good luck..