They aren't keystone insterts, the wallplate is molded for the 5 speaker terminals.

I don't know how else to help you out...I'll take another look at it this weekend, you may be able to get rid of 2 of the terminals, then just get a regular coupler for the rca cables, and if you can fit the tip of the rca cable thru one of the holes that the posts were in, you could couple the rca cable with the in-wall rca cable through the hole for a clean look.

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