Try your Pioneer centre. If the tone isn't right, you can always switch to phantom mode.
The Onkyo has about half the dynamic power into 4Ohms that my cheap Denon has. I would expect that if you plan on pumping up the volume to ridiculously excessive levels, it would shut down particularly if you don't plan on buying a sub. But if you run it at moderate levels and are crossing over to a sub at 80Hz, you will not have a problem. Also make sure that it's ventilated adequately.
For $400, it's a heck of a deal. And if it doesn't "work", you can always take it back.
