His router is tri-band though meaning it has 2 5ghz transceivers.
Unfortunately, for many models - like the Linksys WRT 3200ACM - that second antenna (technically the third one if you include the 2.4Ghz one) doesn’t function at all without the manufacturer’s firmware. It’s a dead stick with any third-party firmware, and is 100% software-enabled.
I have found this fact to be reliable whether it is DD-WRT or OpenWRT, and across several different manufacturers including Asus and D-Link.