"Best" is a relative term. The Onkyo system mentioned is 7.1, THX certified (not that big of a deal really), and their most expensive HTiB to date. I'd listen to it first, and comparable other ones from Denon and Yamaha, and then decide if it is the "best".
^^^ I agree the OP should go listen to various systems. I do believe the 9400THX is the best HTIB on the market.... But the point I was making is the OP asked which is the best Onkyo HTIB. I have heard all the Onkyo systems and IMO they all sound really bad except the 9400THX. It actually sounds pretty good especially at that price point.