I believe what TLS Guy is saying is that if the speaker's internal amplifier is not well designed they can be driven from the output jacks. If this is the case putting a Y-cable on the left and right outputs could allow them to essentially drive each other which would end up summing the signals to mono internal to each speaker.
Hope this is correct and clears things up a little.
HT: Samsung LN32B460 32" LCD (greyscale calibrated) | AVR: Yamaha RX-V765 | L/R: Emp E55Ti | C: Paradigm Center 1 | Rears: Sony Junk | SW: Klipsch RW-10d miniDSP | Sources: Acer Revo Ion running XBMC with mySQL library server and 4 TB HDD, PS3, Technics SL-Q2 TT | 2x Aura Pro Bass Shakers
Bookshelf: Yamaha RX-V992 | Paradigm Mini Monitors
Shelved for now: Paradigm 11 SE Deluxe