It's more important to match the front three speakers. Very little program material actually comes out of the surround speakers in most circumstances. It's usually just ambient noise, etc. with the occassional explosion or such. The exception would be if you listen to multi-channel music on SACD or DVD-A. Then the surrounds take on a greater role.
If the BPVX are working properly, I wouldn't be in a rush to replace them. Of course, this is all dependent on your setup, the room you're in and your expectations. Can you fill us in a little more on your current arrangement regarding the room that the system is in? Also, what are your expectations for a new set of surrounds and what are the current surrounds not doing that you would like to see in a new set?