Right now sound is from LCD only-model LG70. No budget right now to substanially upgrade existing equipment. I have a decent Denon receiver-older model DRA-425. Speakers are Polk audio monitor series M3. I'm interested in purchasing a decent center channel and was wondering can LCD be hooked up to this and then I would hook up the polks to the receiver or is better for me to hook up center to receiver also since it can have A and B speakers.
Also, what's a reasonable center speaker in the $250 range??

Why are you thinking about a center channel when you just have a 2 channel stereo receiver? And as far as hooking it up to the TV, no, you cannot. Speakers need amplification.

When you have the funds, start by upgrading your receiver.

You could hook up a pair of speakers from the tv if they are self powered monitors. Look at Behringer and KRK for instance. However, changing volume might be annoying unless you had one of those tv's that can actually control the preamp output volume (they do exist, but I'm not sure which TVs they are).

But I also wonder like Yosh why you consider a single center with a stereo output. Use a pair.