Seems right hand side is louder, need helps

Hi! Guys,
First of all, I would like to thanks urs helps, I really appreciate. However, I tried many methods but still failed. Hopes u guys can give me some more adv. on it.
( Still using the XLO test CD )
1st step : I tried to swap the inteconnect from left to right, n right to left, just to be sure no problem from my front sys.It happen the same, the center vocal still tends to go to the right. About 1 foot.
2nd step : I swap the speakers, same works , L to R, R to L, , however it still the same, Center goes to the right, stay at the point 1 foot.
3rd step : I swap the speaker cable, same works, L to R , R to L, n yet it still the same, center vocal goes to the right.
4th step : I move around the speaker, just can't work out. I had tried many movement, but failed.
So My Q is that, if I want to get back the vocal to the center from the right, wht shd I do, I had the identical on both side, as this sound room was special designed to be identical, on both side of the wall, as well as ceiling, floor carpet, from wood wall.. Thanks again from the fans above , n just need more adv.Thanks again!

Mike, if you move the speaker over 1 ft, does centering do the same? Also, have you tried actual source material and it still do the same? Could also be that your balance pot is off, or your gain control(s), you don't mention the components.
Have you considered the possibility that you might have ear wax? It happened to me before.
Have you measured the response? You should use a test CD of some sort and plot the response with an SPL meter and determine if in fact you are really have this problem, or is it the "ear wax" syndrome (kidding aside--this really can happen). If you measure the response and find that a particular frequency area (say 1000-5000 Hz--where vocals typcially are) is lower on the left side, then you may have room response issue. Is the room exactly symetrical (this includes behind the listener as some sound is reflected back to the listener)? At any rate, measuring the freqeuncy response of the room of each loudspeaker independently should give you a very good idea of what exactly is going on. It then might require some room treatment to compensate.
Any chance that there's a large reflective object on the right side of your room? Like a large screen TV? Mirror? Window? That happened to me, and drove me crazy until I draped a blanket over the TV and the problem went away! It sure sounds like a room interaction problem to me.
Good luck,
I ve nothing on both side, this is a room for Hifi only, no TV, or other things.2 side r identical. However I just can't get the centre vocal.Just wonder if I want to get back the center focus, which direction shd I go either 1 side of the spk.Thanks!
Have you tried a different pair of speakers, then amp preamp etc, to eliminate the possible mechanical problems? Then, if you speakers are on stands, have you checked how firmly they are contacting to the floor?