aramar wrote:

Is front center channel sufficient?

No, but it beats the heck out of nothing.

This may sound weird but I am severely limited in space.
The TV in our family room is located above a fireplace.
I have space to install a center channel just under the TV.

IMO, this should be done forthwith.

The speakers in the TV are located on the bottom of the unit
and it provides ok sound but it is a pain because I have two
back speakers controlled by a receiver.

The front and back speakers should be controlled by the same entity.

So everytime I have
to change devices DSS / DVD / VCR I have sound level issues
and it takes two remotes to correct this.

Not nice!

I have no room left or right of the TV for two front speakers.

What about elsewhere along the front wall or side walls near the front
walls?

I am not
a sound perfectionist so getting something to work is more
important than having it sound perfect. I considered using
the TV as the center channel (again the sound is ok from it)
but cannot figure out a way to connect it to a receiver.

Ultimately that is probably a good thing. You've already pointed out some
very fundamental problems with this approach.

Someone said it can be connected as the center pre-out.

Perhaps.

Many people said don't go down that route instead get a
center channel.

Easy to agree with. Center channel is also known as mono. Frankly, good mono
is far better than poor stereo. Mono plus surround could work better than it
seems on paper. You probably want to figure out how to mix some sound from
the front into the rear speakers.

You might even get some advantage out of having the front channels feeding
speakers in or towards the rear of the room to enhance the spatial effect.
This is meatball surgery - we're just throwing sound around trying to get
the most pleasing effect. However the basic is there - good mono plus some
kind of spatial effect, beats bad sound and very inconvenient operation.

Will a center channel be sufficient or should I just find a way to hook
the receiver up to the TV?

What's this about "sufficient". You are severely constrained, so the
question at hand is not "sufficient" but "improved". A good center channel
should be an improvement. Take the good that you can find.

About your left and right front situation... Is there a chance that you
could do something kinda Bose-like (wash my mouth out with soap!) and bounce
the left and right channels off the side walls, using speakers mounted under
the TV? To have the required directionality,the speakers would have to be
other than tiny.

What keeps you from putting up other speakers in the front of the room?