Suggestions for echo dampening

I've been lurking here for a while gleaning useful ideas for my little home theater project, but I'd like to seek some specific guidance on audio setup.

The room I'm using is smallish and produces echoes like mad. I need to mitigate this as much as possible on a shoestring budget. The audio is coming from an Onkyo HTS790S with stock speakers, so nothing really high-end. Here's a diagram of the room and various photographs for your reference (pay attention more to the later photos as they show the mounted speaker locations).

The room is 8 feet high to the tray, and another 9 inches to the ceiling. The diagram is more or less to scale except for the exaggerated size of the speakers (in green). I'm thinking that the sharp corner on the one side of the room may present some interesting acoustic issues. I planning to mount the AV components in this nook on some shelves I'll build. The dashed lines represent doors, two swinging (one I have to reverse) and one sliding.

My current strategy for reducing echo is to put down a bunch of thick carpet (like a Frieze) on the floors, and to build a few large absorber panels for covering the two walls adjacent and perpendicular to the screen (I'm intending to use similar construction to this). I can potentially build more panels for "hot spots" or use a different construction if anyone has suggestions on this matter. I'm also hoping that using very soft furniture (whose exact construction is yet undecided) will help disperse some of the sound in the rear of the room.

I'd appreciate any comments on cheap strategies for improving acoustics (mostly echo, but I'm just as interested in issues you may foresee with frequency response) in this room. I'm inexperienced with acoustics, but I have a pretty good ear, engineering experience (microelectronics, though!), an SPL meter, and am capable of building whatever is necessary. I was contemplating making some simple ceiling-to-floor curtains to border the entire room in order to provide a textured surface to disperse more sound. Will adding such curtains yield reasonable echo improvements? It would require a lot of cloth and I would just as soon not do it if it won't help significantly. If this is indeed a good idea, can I get any comments on cloths (fiber density) that would suit this purpose well? I would also like to do something about the big sliding glass doors, which are wonderful mirrors for sound as well as light. I'm thinking about placing retractable curtains in front of these, but again am not sure of whether this will provide a reasonable reduction in echo.

Apologies if much of this is covered in other threads; I have done a lot of reading here, but I'm a little overloaded with information and would just like some input on the route I'm looking at. If you require any more information, I'm happy to provide it. Thanks so much for your assistance!

Lot of good info in that article, thank you. It looks like there's a place I can source both the 3 and 6 pound densities of rigid fiberglass locally, so I'll try to get a price quote on the stuff tomorrow.

Edit: Any suggestions on the big glass doors? I really can't place fiberglass paneling over them...

Sadly, the speakers are mounted directly above the doors on either side of the room (you can see from the pictures I tried to link in the first post; sorry I can't create proper links to them yet). Unfortunately there's not much I can do to move them due to the hilarious amount of fun involved in fishing wires through finished walls and the rather tight space constraints of the room. I understand that they are mounted in less-than-ideal locations from an acoustics perspective, I'm just looking to do the best I can given my space and positioning constraints. I also have the lady to please, which makes it difficult enough to justify a couple hundred dollars of insulation and "strange panels" hanging from walls, much less making any structural changes to the room (I'd never get her to let me move a door ).

It may be possible to tilt the side surround speakers (ones above the doors) down a little bit, but that's about all I could do.

Do you think heavy curtains covering the sliding doors will help echo at all? I would think that they might diffuse mid and high frequencies a bit, which is mostly what I'm concerned with at those locations.

Thank you once again for the help, I'm planning on making some HF absorber panels out of the 703 fiberglass once I get some carpet in there and maybe some bass traps if I can find the space (corner traps are pretty much impossible).

No, the left and right surround. You can see the problem speakers in this poorly exposed photo and this one. Fortunately the front left and right speakers are placed right at ear level.

I know, sadly it's either this or stick speakers right in front of doors that are used for room entry/exit (see above photos). This is why I mused earlier about tilting these two speakers downward slightly.

This is a person who can't tell (or at least won't acknowledge) the difference between a $10 pair of earbuds and some Shure studio phones. I'll do what I can, though.

Very good, I'll make something out of a heavy soft cloth. I can include its light-blocking benefits in the sales pitch as well (a little light leaks through those sliding doors).

*shrug* It's all about compromises. As I stated, this isn't high end audio by any means (receiver + speakers for about US$350, though they do sound quite nice for the money), so I think some echo reduction here and there is adequate.

Thank you!