JoninFlorida,
Before the era of discrete Dolby Digital 5.1, Yamaha always promoted the "presence" speaker setup, which did indeed widen and make the front soundstage more "expansive" and spacious, a significant improvement over the old Dolby Pro Logic processing. If memory serves, the extra pair of front presence speakers are driven from their own amp so they should not present any impedance problem.
In my judgment, the "presence" speakers are not required anymore and I suspect they would muddle the front soundstage. Besides, it's a Yamaha proprietary format and not the way movies are mixed. You can always try it if you like.
By the way, Yamaha is still iffy re driving 4-ohm M80s and the older models definitely did not do so. If you want more punch, get the M60s, which are an easy 8-ohm load.
And don't connect speakers in series if you want fidelity and accuracy. The impedance curves of each speaker will interact and alter frequency response when speakers are connected in series.
Regards,
