New Center Channel Needed???

It actually sounds like you have a DSP issue. What surround format are you using? What size speakers settings are you using? Any other sound processing things you're using?

*edit*
whoops, I read your post wrong. I thought you said you turn up the center channel volume, but instead you meant MV (master volume)

Actually the Paradigm Cinema 70s are rated @ 15-80 watts. I doubt your Sony will put out 80 watts with all channels driven on a good day. Sony puffs their power specs - less so on the ES series but I doubt it'll get 120wpc with more than 2 channels driven.

The problem with such small speakers is the sensitivity levels - at about 87db (84db anechoic) more power won't solve anything. These aren't speakers for large rooms.

You should be able to solve this by just turning up the center channel volume trim level. Center channels are usually set up with room correction programs at 10-25% higher volume than the L/R front speakers to eliminate the dialog getting lost in the mix regardless of how much sound is coming from the other speakers - even during quiet passages.

What is the room like (carpet, plush couch, fabric on walls, tile, reflective surfaces, etc..? How do you have your center positioned?

Ron

The lower the sensitivity of a speaker the more power is required to maintain a certain sound level (SPL). At 87db and only able to handle up to 80 watts they max out quite early. You may be experiencing distortion and not just high volume levels.
Look at it this way:
At 87db one Cinema 70 puts out 87db at 1 meter with one watt - to increase the spl to 90db takes 2 watts (double the power for every 3db increase) - still at 1 meter (this is a constant)
etc etc - but what you need to remember is for every meter you move back from the speaker you lose ~3db. If you are sitting 4 meters back - ~17' you lose SPL very fast - a small speaker can get lost in a large room - and thats what you may be experiencing.

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From MichaelJHuman's excellent AVR FAQ - a word on SPL

Speaker pressure level; Speaker efficiency 85 dB; Measured one meter from speaker
Input Power (in watts) -> Speaker Pressure Level (SPL)
1 -> 85
2 -> 88
4 -> 91
8 -> 94
16 -> 97
32 -> 100
64 -> 103

Speaker pressure level; Speaker efficiency 90 dB; Measured one meter from speaker
Input Power (in watts) -> Speaker Pressure Level (SPL)
1 -> 90
2 -> 93
4 -> 96
8 -> 99
16 -> 102
32 -> 105
64 -> 108
.
.
.
100 -> 110 (approx)
120 -> 111 (approx)

You should notice that it takes very little power to hit 90 dB. We will hear 91 dB from four watts of input into an 85 dB speaker and 90 dB with with one watt of input to a 90 dB speaker. Obviously sensitive speakers make a difference.

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You should try adjusting the center channel sound level - higher than the front L-R by 3-5db to start and see what that does for you before rushing out to buy a new center channel. If you determine you need a different one find a Paradigm speaker to replace it that will timbre match with your L/R speakers.