Center channel matched with Fronts??

You will be disappointed.

All speakers should match. Identical if possible.

For 5.1 try turning your center on end (the tall way). Physically set the LCR speakers all the same distance from your chair say 12' radius for example. Make sure to change your LCR distance settings to zero in the processor if you try this.

What is your processor amp/receiver combo?

I would say that if you feel the speaker is too forward now and you leave the center and replace the L&R fronts.
Make sure you buy a model of speaker that offers a matching center, because you will be back to get it later.
A forward sounding center speaker that doesn't voice/timbre match with the LR's will be in your face. I also agree match the rears, expecially when listening to a DTS soundtrack. All MHO

I had the pretty much the same speaker setup and thoughts as you (Monitor Audio Silvers and matching Silver Center). I thought the MA center was very nice for theater/tv, but hated the silver 8's because they were too forward/bright. I contemplated keeping the center, but sold it off as well when I picked up some quad 22L2's. That said, the Quad center is smaller (smaller 5 1/2" drivers I believe, compared to 6 1/2" drivers in the MA center). You can do quite a bit to help fill out the center channel sound by properly adjusting speaker crossover settings along with the subwoofer.

I set my 22L2's to "Large" on my processor, the quad center to small (crossed over at 70hz or so). This essentially pushes everything on the center channel below 70hz to the sub and lets the L/R channels go full. I use a fuller sounding IC to help beef up the center channel sound (I went with a single Cardas Golden Cross RCA). Then tailor the sub output to just fill in enough low end response so voices sound full/natural (making sure it's not crossed over below 70hz or you'll have a gap).

I'm running 200 watts per channel to the center/surrounds via a Sunfire amp and 250 watts to the L/R via an MF integrated. Key thing is having enough power, particularly if you're not crossing over your main L/R speakers below 70-80hz, otherwise it may sound thin.

As for rear surround, maybe I'm not as picky but I just went with a cheap pair of paradigm bookshelf spkrs. As long as the amp is beefy enough and the pre/pro is decent, I've always thought any good rear surround speaker will do for me.

I think the advice given by steuspeed is correct;if you can't match as in my case I was advised to run center channel as phantom; I did until I could buy a matching speaker.