I want to upgrade my center to a VP150..its 6 ohms..the rest I have are 8 ohms..will this pose any problems?
You should have no problems. Matching speaker impedance is not very important. It should only be a concern if you get into speakers such as the M80 that present a 4 ohm load, some very cheap receivers have issues with overheating or over-current conditions in that instance.
But, a 6 ohm center speaker. You are good to go!