Well you do the best that you can then. Perhaps this speaker will sound close, I don't know. Its important in movies and music IMO--when a helicopter goes from left to right, it should sound the same coming from the center spkr.
If you mostly do movies, its not essential to timbre match. Most of the time different content is coming out of different speakers, so no biggie. However if you do music, you want everything to match tonally, so its more essential to match at least the same brand and speaker line, if not all the same speaker model.
Around these parts people just suggest staying with the same brand and line to avoid any issues down the road.