Speaker and Sub placement

Search AVS for "sub crawl", which is a technique to identify the best placement for your sub. Unfortunately every room and sub interact differently, so it's hard to say what is the best position based on pictures or floorplan.

Shelf placement, or any non-floor type of placement, is not inherently a no-no for subwoofers (in some cases it's even the best place--it's hard to tell without empirically measuring and experimenting). However, placement inside an enclosed shelf or cabinet should be avoided for all types of speakers because it can result in strong reflections that color and muddy the sound, as well as resonances that, having no need to get overly technical here, can make the speaker sound distorted and "honky." It's much like the acoustic issues that all rooms with bare, untreated walls have, only greatly magnified.

OK, enough with the doom & gloom--try the speakers in their intended locations first to confirm or deny any acoustic issues with the enclosed shelves; yours are relatively large, so maybe it's not as bad as some of the cases I've seen. Be sure to place the speakers as far forward as possible, but obviously not so much that they'd tip over , as they're probably somewhat front-heavy. Also avoid placing them in the exact center of the shelves, which may result in stronger resonances--move them closer to the TV. If they sound OK to you when compared with how they sound, say, when placed at the edge of a table, then great, otherwise you may have to line the shelves with something that absorbs sound. Speaking of which, if your floor is hardwood, you may want to consider placing a rug in front of the entertainment center, as reflections off a bare floor can often be harsh; even if the speakers are mounted high enough to avoid this, it is still helpful to cover at least one side of the room with something that absorbs sound and thereby diminishes echoes.

As for the subwoofer, try placing it in a bunch of different locations to find out where it sounds the best. Does your receiver's YPAO function show you any graphs of what the response was before equalization? If so, then you can use that to help determine the best placement for the sub--look for the flattest, smoothest overall response with the fewest or preferably no large dips. Don't rely on automatic room correction alone--sometimes these systems do crazy things like use massive gains to try to fix a problem that can only be effectively fixed by other means, and this can potentially lead to things like power compression (making your sub less capable than it really is) or even, in the most extreme cases, damage that would not otherwise have occurred.