Center channel Impedance.

[E-Stat]

Although amp will not have trouble driving the load, but by connecting speakers in series, it does change the electronic characteristic of speakers.

Isn't that essentially what I said in the two sentences you quoted?

I tried two speakers in series, and notice that not only it pretty much kill speakers bass responce, it made them sound lifeless.

For starters, bass response for the voice track really isn't that critical. You might be surprised how many speakers use series wired components. Aren't you one of the Roger Russell disciples? You do realize that his IDS speaker is wired thusly, right?

rw