Wow sorry, I thought I typed that in, but they are the tSc p6-pr.
I have reviewed your speakers technical details. There are only sparse details available.
It is clear that your mains and center speakers have very different sonic signatures, by your description. This is to be expected at the budget end of the scale.
Basically your three front speakers need to have the same sonic signature, or your front stage will discontinuous. Matching speakers is known as timbre matching, which really means having front speakers with the same errors as far as possible.
The TSC speakers have a reputation of being on the bright side, but that seems to be the sound you prefer.
You have four options.
Get rid of your center speaker and go to a phantom center.
Try and find a matching TSC center on eBay. TSC have folded their tent.
Get rid of your TSC p6 speakers and purchase Polk Tsi 100 speakers for your mains. This may not be a good solution for you as you don't seem to like the sound of your Polk center.
Ditch the whole lot and start again.