"Am I correct in understanding that all I need do is use center channel wire, hook up 1st LM1 and continue wire to 2nd LM1 effectively wiring in series? If the result is not pleasing then I can fall back to using 1st LM1 as center."
No, that's parallel. You can try it that way but your amp may strain a little. For series do this: 1. Connect a speaker cable from the + on your amp to the + on one of the speakers. 2. Connect a speaker cable from the - on your amp to the - on the other speaker. 3. Run a speaker cable from one speaker to the other connecting it to the unused binding posts.
As far as the volume issue goes, I meant that using 2 speakers for the center will take the demand off 1 speaker used as a center. That's why I suggested the test in my first post. Listen to some music just using your main L and R front speakers. After a minute or so, just unplug 1 of the speakers and listen to it. If you do that, you will see immediately what I am talking about. Just listening to the 1 speaker play music, you will see how hard that single speaker has to work to keep up with the main 2. Its just a rough test. When you are watching a movie, different info is sent to the center channel, so the test isn't 100%. That said, its still a very good indicator as to how the front and center speakers interact with each other.