Wireless Performance Tuning a Dual Router Setup

I'm looking for a little help diving into advanced wireless settings... everything is working fine now, but I'd like some guidance on settings to improve handoff, reduce interference, increase wireless speed, etc.

Here's my setup:

• I have an Asus RT-AC68U as my primary router, connected to my DSL modem.
  • 2.4G radio:
    • Mode: Access Point
    • Network Mode: Auto
    • Channel: 9
    • Channel Width: 40Mhz
  • 5G radio:
    • Mode: Access Point
    • Network Mode:...

Wireless Performance Tuning a Dual Router Setup