To uber and bstatmeister:
That's what I do, so long as the pre signal is controlled by your volume control.
The bad news is you have no control over the satellite's frequency response. On the other hand, you also can't mess it up.
Since the miniDSP is so flexible however, you can really tailor the sub's output for maximum integration with the satellites.
If your current satellites are ported, you may find it easier to integrate by stuffing those ports closed.
The key here though is measurement and delicacy of setting. Worthwhile reading the white papers on their site and hanging out in the Room EQ Wizard forums. I use OmniMic for my measurements. It's a little more expensive but I love how easy everything is and the built-in DSP curve simulator. It lets me try out different curves and see them before I copy them to miniDSP.