If you want speakers that can really cut through the clutter and have a strong presence in the voice/mid+high range, the horn loaded Center and Front are worth considering.
But, they are not exactly giving these away -
Klipsch Reference 52 II ($296/each) -
Klipsch Reference 62 II ($399/each) -
Here, if you scroll down, you can see the entire Klipsch Reference II series line up -
The Infinity Primus PC351 is a good center in its price range but it is BIG. Make sure you can handle the size.
Infinity Primus PC351 ($199/each) -
I think we need to know specifically what Sony Center you have now, and we need to know the rest of your system. That will lend perspective to our recommendations.
In the short term, there is nothing wrong with a mismatch between the Front and Center. But in the longer run, you are going to want them Tonally matched. So, whatever decision you make now on the Center, somewhat dictates that that is the direction you go in the future. For example, if you buy the Klipsch Reference Center, that implies when you buy new front, they will also be Klipsch Reference speakers.
Unless you want to consider this new Center speaker a throw-away. Use for now, and ditch it later when you replace the Front Three (left/center/right). Though best to make a decision now that directs your choice in the future, so you aren't wasting money.
So, as well as the equipment you are using now, we need some sense of where it is you intend to go in the future. The nature of the system for the future and how it will be used. Some of the suggested speakers are very big. That would be fine in a larger home cinema room, but a bit overwhelming in the average living room, especially if you are married.
So, we need to understand both short term and long term goals including your budget.
Keeping in mind, the choice you make now, somewhat dictates the choice you will have to make later.