Audio Systems: Adding speakers to my HT, center channel speaker, amplifier system

Question
I have a 5.1 600w home theater amplifier and would like to add 2 more in-ceiling type speakers.
The in-ceiling speakers are 8 ohms and have double voice coils; my amp works at 8 ohms.
Is it possible to wire them in series to my center channel speaker or to the front channel speakers?

I'm basically concerned about the impedance load and not burning my amp, but I would like to safely get the most volume out of the 8 speakers.

All 6 speakers that come with my HT package are standard single voice coil.
Thanks in advanced.

Answer
It is very dangerous to load an amplifier with an impedance that is lower than the amp is rated for.  If the amplifiers are rated for 8 ohms and you already have an 8 ohm speaker connected and then add the additional speaker (with the voice coils wired in series) the load on that amp will now become 8 in parallel with 16 ohms yielding a resulting impedance of:  5.4 ohms.  This is too low.  Therefor, if you disconnected the factory speaker and used only the new DVC unit on that channel you would be okey.

Let me know if I interpreted your system correctly.  If you would give me the make and model of the surround sound receiver I could check it for robustness.  A good Sony or Pioneer unit could handle the dual load well in all probability.  But if the amplifier system is a Coby or some other lower end make you should be generously above the impedance rating so as not to over stress it.

Hope this helps. Don't hesitate to ask for further clarification. But if you do please give make and model numbers for the receiver and the new speakers so I can do the engineering thing with them.

C