Help with Surround Speaker Placement - Pics Attached

I'm curious to get some opinions for the optimum placement of my surround speakers. As you can see in the attached pictures, for being a pretty dang rectangular room, it has some oddities with the staircase up to the kitchen/main floor living room, doorway to the utility room/basement, and fireplace. The room is 28x18 with 8' ceilings, minus a nice 9' wide portion in the middle that is encased ductwork for the top-level. Therefore, in that 9' wide area, it is a 7' ceiling.

Also shown in the pictures are my teeny tiny Onkyo HTiB surround speakers. Squint, maybe you can see them! I'm so excited to get everything hooked up with my new Polk M70s as L/R, CS2 as center, and M30s as rears. Regardless, as I think is visible, the current setup has the surrounds at a slightly different height, but not drastically different. With a now "more legit" system, I'm more concerned by the fact that the surrounds aren't outside of the entire seating arrangement. They are positioned pretty well for the couch, but the two armchairs on the ends are outside of them. I'm assuming that's bad?

Moreso than that, is it worth the wire run to get them all the way in the furthest outside corners? If I go to the those corners (marked in the pics), mind you, they are still going to be at a slightly different height and depth (depth being from the back of the couch to the face of the speakers). Because of the recessed lights around the mantel, and the fireplace/chimney, the right surround speaker location will be about 1' lower and 4' forward of the left surround speaker location. I'm also slightly concerned that these new locations are going to be SO far away from the couch, and the "better over here?" location for the left surround speaker is going to be so much further back than it is today. Can the M30s handle that?

Thoughts? Comments? Are the other locations noticeably better than the current spots that the Onkyo's occupy, or am I better to keep them where they've been?

Thanks in advance!

I had contemplated that as well, but didn't know what benefit I would get with them being that far out (which is my same concern as burying them in the corners too).

On the right surround speaker side, the bright light you see is coming from a sliding patio door. But I do think I could get something aligned decently with the seating positions if it was above the "landscape" frame on that side.

As for the left surround side, the door you can barely see is a door out to the garage, but like the right side, I think I could get something pretty decently positioned between the door and the Budweiser mirror.

Speaker wiring might be a chore, as if I go all the way out to the end walls and down, I'll have to somehow pass over two doors (patio door on the right side, standard door to the garage on the left), but I could probably get something worked out.

As of now, my fronts are at the edges of the entertainment center. Don't point and laugh, they are from the Onkyo HTiB that the same surrounds came from 5 or 6 years ago. Can't wait to get the Polks hooked up, once I get the new receiver. I'll post a pic below that I used in another thread trying to figure out how to handle this new plasma that I'll be ordering soon. To be honest, I have never even considered spreading them out, but when this new system goes up, it might be a good thought, because as I sit here and look at them, they aren't really "outside" of the two edge armchairs. Good thoughts!

All of this talk is certainly only "planning" right now. The new speakers are here, and the receiver and Panasonic plasma will be coming "soon", probably within the next 4-6 weeks.

Again, I'm very grateful for the help, and I hate to do this, but I'm going to revive this thread, as I have a big weekend in store.

Taking delivery of my 65VT30 tomorrow, and will run the slides as suggested for at least 100 hours. In the meantime, I'd like to get some wire fishing and "prework" done while I can for my Polk surrounds (Monitor 30s).

With that being said, I'll post some new images below, and would like some feedback on the proposed locations.

I didn't want to clog the picture up more than it already is, so here is a little color legend. The blue is where today's crappy Onkyos are. I'm now considering the green areas, as that will help spread my spacing out (roughly from the 8' I have today to almost 12.5') and will have them at a somewhat even height and depth. My big concern with this area is the doorway down to the utility room/basement. Does that protrusion hurt the effect of the speakers? Will this "depth" be a detriment, as opposed to having the speakers up flush with that doorway to the basement?

As much as I'd like to mount these way outside where I had originally hoped, I have come to realization that it just isn't feasible, and there is no way to get the wires out there cleanly (or cleanly based on my capabilities). Therefore, I think I'm stuck getting something through the encasement for the ductwork and the I-beam.

And finally, the red circle is a random idea I had for the sub (Klipsch RW-12d). I know the sub crawl and all that entails, I'm just curious if this cubby hole would even be sufficient. It's intended for firewood, but is kind of a lost space. After some measuring, I realized it would fit in there with sufficient (I think?) breathable space. I'd have about 6" of extra space on top, 6" of extra space on each side, and about 5" of space behind it if I put the grill somewhat flush with the opening. And there is power in there, and I have a plan to get the cable over there. My main concern is it is plywood finished on the inside, so how "boomy" would it be? Is that too tight of an enclosure?

Here are the updated pics. One with my new colors, and one unedited, since my updates make an already dark picture even harder to comprehend:

Thank you. It seemed too tempting to not ask the question about the sub, but at the same time, I knew it was a bad idea from the beginning. I just hoped it would have worked......