If you want better soundstage and imaging etc, the way to do that is speakers.(yeah I know
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Electronics won’t be able to help with that. So, what you can do for free, is experiment with speaker placement. Try different toe in, and moving away from the front wall etc. Try some diffusion/absorption on the side walls like a blanket. Then you’ll have an idea of spending money on acoustic material, or diy will be worth it. All those things are free to try, and will be better for what you want then the proposed electronics. Also. If you’re on a leather couch with a reflective surface, try a blanket on the back. This can help with smeared imaging. Especially if you sit deep in the cushions. If the AVR is capable, I’d consider undoing the buywire and install a pair of height speakers. Jus sayin...