If you really want to take a deep dive, read about sound proofing for home theaters. For higher frequency stuff, it’s not too hard. Air seal between the 2 units, physically block any intrusions, foam around boxes, caulk between the floor and your drywall, etc.
For low frequency, from mens voices down to low bass stuff, you need mass. So double up your drywall with 5/8. Or change out the insulation from fluffy fiberglass to mineral wool. Or decouple the entire wall with another wall. But doing that, do you have enough wire to extend out your electrical? What about other finishes? Doors, windows, etc?
I would air seal to your best ability, then look at green glue between another layer of 5/8 drywall. That should help.
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