I recently got my first stereo equipment, which is not the best, but I am really happy with it for the price I paid

I got the JBL ProPack II, which included a reciever, DVD player, and 5.1 speakers. Like I said, I'm loving it, but I think that the center channel could be improved. Plus, I'll only have to buy one speaker and it won't cost too much!

But I was wondering, since I have these little satalite speakers, will a big center overpower everything else? Or will this not be a problem, since all the speakers wil have the same (100w) to them?
For reference,
here are the speakers that came with the HTIAB
and
here is the JBL S-Center that I was looking to buy (only $129 on etronics.com)
Also, the reciever can set each individual speaker as 'large' or 'small'. I assume if I was to replace the default center with this new center, I could change it to 'large'? Or is this still relatively small compaired to other, better things?
I'm really new to this, so sorry if these are stupid questions!
