Rear surround speaker placement: side walls or back wall?

The surrounds in a 5.1 system are intended to be mounted on the side walls facing in (option 1). The layout of my room is very similar to yours, and one of my rear speakers is farther away from the MLP than the other. When you run the setup on your Denon, it will compensate for this by bumping up the volume on one of the surrounds.

It is also recommended that the rears be mounted above ear level.

Since your couch is right up against the rear wall, mounting the surrounds either on the side or rear wall would work, so long as they are angled to face the MLP if mounted on the rear wall. The surrounds are meant to be parallel to the MLP, or a little bit behind.

Since you have bookshelves i.e. direct radiating speakers, they should point towards the MLP.

In an HT surround system, diffusion is one goal for the surrounds. If these are direct-radiating speakers, don't aim them directly at the listeners. Letting the sound reflect off the back wall and/or the ceiling can actually help, an effect that can sometimes be achieved well enough just by corner-mounting.

If a system is used much for multichannel music (eg, 5.1 SACD etc.), this diffusion can work against you, and compromise is necessary.

PS: Just to be pedantic, you're talking about the "surround speakers." The "rear surrounds" or "back surrounds" are the additional channels in a 7.1 system. This distinction can matter when people mistakenly connect their surround speakers to the "rear surround" terminals on their AVRs.

Well, this is one of those debates. In a movie theater, there are multiple surround speakers spaced around the back and sides of the screening room. Sound mixers, knowing this, tend to create diffuse, spacious, ambient surround tracks that don't localize specific sounds.

Reproducing this effect in a home using two speakers means either using speakers that themselves diffuse the sound -- which is why bipole and dipole speakers are often used as surrounds -- or by orienting direct-radiating speakers relative to the walls and/or ceiling so they use boundary reflections to create diffusion. In all cases, no speaker would be aimed directly at a listener.

But do you want this effect in your HT? Well, that's up to you. There are some kinds of program material -- notably multichannel audio recordings -- for which the optimal speaker configuration is five identical full-range speakers. Hard to set up in most rooms, but a matched set of direct-radiators and a sub comes close. For this you'd want all the speakers aimed at the listener... but that same system would be sub-optimal for most movies.

Add to this the differences in how we hear sounds that come from in front vs those that come from behind -- sounds from behind are harder to localize because of the way we're built, to be crudely over-simple about it -- and you come around to the fact that there are a number of ways to achieve satisfactory surround sound, all of them room-dependent. Generally, though, the advice you've gotten here -- mount the surrounds high, aimed in from the sides as in your option #2 -- is good. It would be better if you could get that couch away from the wall, but it's a small room for that much seating.

If you can come up with a way, using stepladders perhaps, to temporarily position your speakers for experimental listening, you can find the answer that sounds best to you.

Isn't the couch facing the screen the primary seating? Why aim the speakers (a) away from the primary seating and (b) away from any nearby reflective surfaces that could help diffuse the sound? It seems like your plan is to aim them directly at an empty space where nobody will ever sit, and to create as little diffusion as possible.

If anything, I would move them a foot towards the front of the room and aim them slightly back towards the back wall, and even a little upwards, so that you'll diffuse the sound off the back wall and the ceiling. Failing that, just aim them straight across -- right at each other -- and mount them close to the ceiling.

Unless you and your family are freakishly tall, a speaker aimed at a point 8 feet above the floor is not aimed at a seated listener.

Assuming you are not using ported speakers or some other design that requires some minimum spacing from the nearest wall, then yes, aim 'em high and place them near the back wall. The direct sound from the nearer speaker will pass mostly over your heads and you'll hear a diffused mix of reflections, and more of the direct sound from the speaker farther from you. The result will be the kind of surround ambience you hear in a theater. Obviously, don't do this if that's not the result you want.