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.

You can easily get away with a well thought out non-matched center, while there is ofocurse a benefit to a matched model a bit of snob kicks in when people are asked about all matched speakers, mine match as of now but I have had excellent results in the past when older speakers simply didnt come with center options or budget kept a matched center from being possible.
I would choose a carefully thought out non matched center over phantom anyday of the week, if folks sit off axis its not going to work great and even on axis sometimes center info is hard to hear..........the center channel is there for a reason, its not just hype. Match all if you can, if you cant from center to rears just audition and you will be happy.......its not as cut and dry critical as many would make you believe and your ears will confirm this!

I bought the RS6 for front L&R and feel they are brighter than I want. I have not bought the rest of the home theater speakers yet. Was thinking of getting the center in either the RS or the Radius 180. Would either work or must I have the silver RS center? For rear speakers I wanted to get something warmer sounding to, hopefully, warm up the general sound. I can't return the RS6's so must keep then for the time being. Was looking at Quad, Dynaudio, PSB, and Era bookshelves in the less expensive lines for my rear speakers. What are some recommendations for warm, smooth speakers and do you think that by having warmer rear speakers, it will warm up the sound and balance out the brightness of the MA RS 6's?

Adding warm speakers to the rear or center will not fix your problem. It's like having 4 different tires on your car. Yeah it goes down the road, but it will never handle very well. The whole idea about surround sound is to create a seamless presentation. No one speaker should draw attention to it's self. Each speaker should image to the next just like a stereo pair. Forget all the marketing BS about special center and surround speakers. All the speakers should be the same (5 2way bookshelf speakers for example). Next best is to have at least the same drivers.

Surround content is approximately 50% center, 40% R&L, 10% Surround. A small center channel speakers will compromise any system. A common mistake. Sideways center channels with MTM driver configuration also have vertical dispersion, yet anther problem. Don't believe me? Turn your LR speakers on their sides and tell me how great they sound. An RS6 is what you really need, but probably not practical standing in front of your TV. If your speaker is too bright, I would start over with different speakers or try changing your electronics. Most receivers are bright and glassy. Better gear help might solve your problem. Sorry, I kind of rambled there...

I challenge all the folks who swear to all matched speakers to identify most any non-matched system put together with even just a bit of care, its not hard to do and it works. Sure all matched speakers are going to be ideal and certain to work best but anyone who tells you this is cut and dry and can never work with other options are either wrong, a snob, just dont know or a combo of all of these. A matched center is important to do if possible but as for the surrounds...they are almost a non-issue within reason as the amount of info the recieve and the placement of them in the room simply doesnt dictate a match, and if I put 10 people in a room that was carefully done without matched speakers 9 or even 10 of them would not pass the test.

Hey Cfunkster, If you get rid of your speakers, maybe you could sell me your center. I guess that is what I need. I can't get rid of my RS6's, they are only a couple months old, and selling them and starting over is a waste of money. They are good speakers, just not as warm as I would like. They only have about 25-30 hours on them, so I hope they mellow out some.