Since Onkyo does give dynamic power specs for that receiver into 3, 4 and 8 ohms for the front speakers you should be OK. If you are using them as rears I would call them. http/www.onkyousa.com/Products/model.php?m=TX-SR333&class=Receiver
The amount of actual power you get continuously will be less but still be adequate. The receiver might run warm so make sure it is well ventilated.