Thank you so much for the replies.
So I got my unit replaced for the new one yesterday evening. Been testing it all day all night, turned out that this unit is much better. The Center Speaker doesn't get any distorted dialogue like the previous one. Still quite surprised why this kind of problem happened and it's considered to be Brand's Hi-End Product as well... this problem should have never existed.
After I tested the speaker... I'm satisfied with it, comparing to the spent money, the quality is there. Still I feel like the high note/audio should have implemented much better than this.... for me, it is not crisp enough and still got some slightly distorted/crack at the very end of those sound. It's not that much, very little but it is there if you monitor or look for it. Bass is deep thought, shakes the whole floor.. very nice.
Still deciding to hang the rear speakers at the back or buy some stands for it.