All the normal caveats apply;
Most importantly, assure every seated position ear height, in each row, receives a clear an un-obstructed path to each of the three front speakers.
Ideally, each LCR is aligned horizontally with one-another, or as close to this theoretical ideal as possible. If a center channel below the screen can't project clearly and unobstructed to the second row, then move it above the screen, and move the remaining L&R up higher as well. I've had much success covering my room from above my display angled down and in, ... PA style. I've since moved to different situation so that no longer applies, however it's easily doable.
With regard to your subs, best practices should be observed. This includes placement dictated by the room's acoustic needs, as measured at the listening position(s). If you have no such capability, I'd utilize a starting point of approx. 1/4 points, width wise, of your room's width. This should minimize differences in bass response across the width of the room, in each respective seat. You really need to experiment a great deal with sub placement, it may be the single most important aspect you can control; ie, the interaction of the subs to the room's acoustic environment. It's all about the room, experiment with placement,...and unless you measure, you're flying blind.
Rom treatment, bass traps, difusion/scattering, and early/first reflections need to be addressed. A phenomenal impact can be attained with a modest DIY effort and expense. The single most important system component is the loudspeaker/room interface.
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