<font color='#000000'>Well, keep in mind two things:
1) A majority of your Home Theater sound is coming out of the center channel (nearly all the dialogue, every on-screen effect, etc)
2) Continuity of information traversing the front 3 speakers is important, as a mismatched set is likely to make the sound jump or dip when traveling from the left to the right.
So its a matter of allocating enough budget to get a decent speaker, and also of being able to tell if the new speaker will sound good with your existing system. Unfortunately, you probably won't be able to bring your speakers in to do a live audition, so you'll need to figure out how to match the tonal characteristics of the new center with your mains.
I can't really recommend anything as I would place tonal matching pretty high on my list and I don't know your speakers. But whatever you choose, perhaps you should hold off for a while and then get three new speakers. I just wonder if a new mismatched center channel will be a good purchase, or if it will create new problems for you.
Perhaps there are others who are more familiar with your speakers and can recommend soemthing that would be a fair match.</font>