Then I'd recommend a Def Tech center. For 5 channel music and HT you definitely benefit from matching speakers in the front. Would you use different brand left and right? Then why mismatch center and mains when they are trying to convey a consistent sound stage and imaging?
With all due respect(really), it does not seem to me that you are upgrading to get better results, but upgrading to get worse results.
Doesn't Def Tech have other center speakers compatible with the towers? Neither of these two center speakers will have any sound quality compatibilities with your current L/R main speakers. So it seems to be you are going backward instead of forward here.
Titan Reference 3D 1080p projector
200" SI Black Diamond II screen
Grass Valley Cell based Pro HD A/V switcher
Audyssey MultiEQ XT32 EQ module
Audyssey XT32 Sub module
9 Onkyo M-5099 power amp
9 Onkyo M-510 power amp
9 Onkyo M-508 power amp
5 custom CAL amps for subs
3 custom 3 way horn DSP hybrid monitors
8 custom 3 way horn DSP hybrid surrounds
3 custom 15" sealed FFEC servo subs
4 custom 15" H-PAS FFEC servo subs
THX Style Baffle wall
Are you using two sets of main speakers? It's not clear to me what you are using right now. I'm not that familiar with Klipsch or Def Tech's different series. The point I am making is the center and mains should be the same brand, same series. So from what you have now of Klipsch and Def Tech, which sound do you like best? Then, take that brand an set yourself up with a matched set up. I wouldn't bring JML into the mix unless you were willing to get rid of everything you have now for speakers and go with a total matched set of JML.