Speakers and what's between them

You should keep sharp edges about 3 feet from speakers... a speaker placed a couple of inches from a TV screen with a 1 inch gap between the two will suffer edge diffraction and may affect mid range imaging and sound stage.

Apart from the above, no is doesn't matter that much in fact it matters less than what you place in front of your speakers or what you sit close too (close to a wall, corner = BAD). Of course the same rules apply as to any surface/furntiure in the room...strongly reflective surfaces (concrete wall) will not absorb bass energy but may reflect it well and therefore will not help to reduce room bass reverberation compared to a wall that is covered in shelves with books.

In my experience I had a TV in between the speakers and it collapsed the soundstage. I've now quit trying to play with home theater and I place my other components on the floor not on a rack between the speakers. This allows much more depth of the soundstage.

also you should keep whatever is between your speakers behind the front edge of the speaker

also you should keep whatever is between your speakers behind the front edge of the speaker

Agree.

Edge diffraction will occur at the edge of your speaker baffle anyway...but at least your speaker manufacturer will have designed for this issue so it should not affect performance that much (it is also a good reason why you should NOT remove a speaker grill unless the manufacturer says you can).

A TV edge sitting an inch or two away from the speaker edge is going to cause the acoustic wave to bounce off it - like a wave coming towards the beach and being interrupted by a pier....it creates secondary waves.

If you were to bridge the gap between the speaker edge and flat TV surface then you would eliminate the problem all together and it might even sound better (as you have removed also the diffraction off the speaker baffle edge)

The alternative is to keep surfaces about three feet away (or as suggested above - well behind the front of the speakers)...by this time the sound has already lost so much energy and it starts to get far enough away so that the secondary waves interfere much less with your perception of the primary energy from the speaker (arrive much later than the primary signal and much weaker) - so it no longer affects the sound stage or image too much.

Ideally;

AA) nothing between the speakers at all leaves you only the edge diffraction from the speaker baffle edge itself.

or

BB) if you are fanatical, then you need to build the speakers flush mounteded into a perfect flat wall (no edge diffraction at all)

In practice you just need common sense....if the TV or stereo rack/cabinet is three feet away or more and placed behind the speakers then it will be slightly in the acoustic shadow of the speaker baffle edge anyway and far enough away that you can forget about it (side walls ceilings and other effects will be just as problematic at this point)!