In general it is better for the L/R and the center to match by being from the same manufacturer and preferably the same model line. I haven't heard any Klipsch outdoor speakers but if they follow the sound of other Klipsch speakers the Ascend probably wouldn't match very well sonically. I did notice that the klipsch kho7 had a efficiency of 92 which is much lower than most Klipsch speakers so the Ascends might do better.
If it were me I would try a Klipsch Synergy III C3 center channel and see how it matched up. Depending on how big a space you are trying to cover the extra efficency of the Klipsch may serve you better than the Ascend.
Now let's see if I flamed for recommending something other than Ascend on the Ascend forum.
Darren
There's no place like 127.0.0.1