No comment on the Klipsch's, but my audition of the Martin Logan 60XT was very nice, and I enjoyed them a great deal. At full retail cost, I didn't think they were worth the premium price point, especially compared to Monitor Audio Silver 500, for example. At the discounted price that they are selling for now, they are a very good speaker.
Between the two designs, you have completely different beasts. My own preferences tend towards 3-way designs over 2-way, and I also prefer wider dispersion over controlled directivity (horns).
YMMV
I agree with Danzilla that you will at least need to match your front 3... I would not put the 60XTs together with a Klipsch center. I am willing to go out on the limb and say they will not have a similar sound quality, if that is a concern to you.
Now...
Enough what?
With the measured sensitivity of the Klipsh 8000RPF at 92 dB, you only need ~32w of power to make them hit Reference Level Dynamic Peaks @ 1 meter... and in a moderate size room with some boundary support, 64w will get you that same level roughly out to 2 meters.
Which begs the question:
How loud do you listen?
I could conceive of the muddled comment, but based on what I know about Klipsch and the review Shady did for the 8000s, flat doesn't come to mind...
Which leads me back to Danzilla's comment about how you have your room and speakers set up. I think you have something amiss, acoustically, and you should first look at identifying that before spending on new speakers.
This could be anything from Speaker Placement, Sub Placement, Crossover Settings, etc.
Looking at proper set up is a FREE UPGRADEm and this is where you should start. Then, consider new speakers if you are not enjoying the Klipsch.