Let's say you have an interview-format podcast with a guest who connects via phone or Skype. Or you have a co-hosted podcast with a co-host who connects via phone or Skype. To record this podcast, you need to get both sides of the conversation on tape.
But "both sides of the conversation" is a problem for the guy connecting via phone or Skype. He only needs to hear your side, because sending his part of the conversation back to him will come through an echo and is a potential source of feedback.
The solution, known as a "mix minus" is a "mix" of you (and possibly an in-studio co-host, sound effects, or other signals from within your studio), "minus" the guy who's connected remotely.
Note that this setup will work with recorders other than the Zoom H6, provided you have both a line out (headphones) and a line-level output (your voice into the iRig 2 interface), but know a line-level output is not a common feature on many mid-price recorders, so double-check for this before purchasing.
Other "Mix Minus" Options
Don't have a Zoom H6 Portable Recorder?
If you record your podcast using a mixer, read How To Connect A Phone To A Mixer.
If you want an even simpler solution for recording remote guests and co-hosts, use a USB mix like the ATR2100 to go directly into your computer and pick one of the following options: