I'm not sure what I need

Yes!  I use a pair of KEF KC62 subs to augment LS50s and they pair very well, as they were designed to do. It’s amazing these little hi-tech subs can deliver both felt and heard pipe organ pedal notes, and can also high-pass to the LS50s. You might take a look at Darko’s You Tube review.

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The KC62s look very good. I'm considering them as well as the REL T7s. 

My room is 14'x16' with an 11' height. Do you think one sub will do it or do I need two?

Start with one and add a second later.  Two usually smoothes the bass.  I think Darko suggests if only one it might be placed between the mains.  Mine are placed on Auralex pads at the bass of the KEF stands, but the pads may not be needed --  I just happened to have a spare pair.

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Thanks. I think I will do that.

I installed the anthem in my system and now I need to connect the oppo to it. Do I do this by HDMI out from the oppo to in on the AVM?

 HDMI-Audio to AVM, HDMI to TV, monitor, or projector.

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