soundstage question

Any screen will compromise the sound quality. Cover it with a thick blanket or similar when doing serious listening. If you can rig up some foam, etc. panels on a removable hook setup, that would be even better and probably pretty easy to make. Cheers,
Spencer

A thick blanket may have too much absorbion...too heavy and too wide. But the screen should be covered.
Panels are best for focusing the image and enhancing the soundstage; some reflective surface is needed.

A wall shelf should be fine as long as absorbion and/or diffusion is used.

4 ft. sounds like a good distance from the wall. Keeping distance from the wall helps 3D imaging, but decreases bass extension.
  If the speakers are close to the side walls, absorbion or diffusion may be needed. It’s also possible that bass traps may be needed in corners if bass does not sound tight. All these treatments (or lack of) will affect the size and shape of the soundstage.

I think it IS a good idea to put your TV in first and then hear if you have a problem. Use a blanket to temporarily cover it. Until you get it, don't sweat it too much.

One rule of thumb I use is this: Room acoustics improve sound stage in the same plane. If you find you lack depth, improve room acoustics behind the speakers and behind you. If you lack width, improve room acoustics to the sides. Height? Same thing. Floor and ceiling.

Asides from the sound stage there's the question of tonal balance, and that is more of a room averaging thing than specific locations.

Best,
E

oh, almost forgot. If it turns out your TV is a problem, two ways to mitigate it without making your listening room look like an abandoned playhouse:

Use standing acoustic panels to the sides, at 90 degrees to the wall.

The other is to increase absorption and diffusion behind your listening location.

One of my best upgrades was to use absorbion on the wall behind me. I hung a large tapestry and it helped define the soundstage and absorbed standing waves resulting in smoother highs.

The op doesn't need to deal with much floor, ceiling, or sidewall reflections---the ET LFT-8's are line source dipole loudspeakers. Behind the ET's is a different story, of course. One thing you could try is a pair of 2' X 4' floor-standing diffusers or absorbers placed either side of the new TV, parallel with the side walls and facing each other, to deal with the back wave without having to move the diffusers between listening and watching positions (read on). If moving them doesn't bother you, place them against the wall either side of the TV while watching it, and move them to in front of the screen for music listening.

Many thanks; your responses are greatly appreciated. I'll take Erik's advise and get the tv in first and then tweak in accordance with your suggestions.  The first issue I will need to address is whether to use a small stand, wall mount or  shelf for the tv.  Any thoughts re that issue and specific recommendations would be appreciated.  I googled  and couldn't find a commercial tv wall shelf so that probably will have to be custom made.