The Stereo Pan switch is unique to the PROFx6v3 (higher models use pan pots on the Combi input channels). Nearly all other compact interfaces assign everything R/L — the odds output to L while the evens output R. My AIR 192|14, for example, 1,3,5,7 output L while 2,4,6,8 are R. In a DAW, this isn't an issue since these are all Mono ins for Mono tracks but it's a reason I'd never bring the Air to a live gig.

The Mackies let you assign a single output to both channels with that SP switch (or the pan pots on the 10 and above). This lets you take either R or L as a Mono for inputs 1, 2, 3 — and no one else does this. Way nice for a live rig. If you plug into both 3 & 4, then those become stereo R/L.

5/6 is a 1/8" TRS designed for your iOS, Android, mp3 player etc. and is always stereo out. It has additional functionality controlled by the Break and To Phones switches. It's not designed to be mixed into the other channels live. I recorded a number of instruments directly from my iPhone and iPad plugged into 5/6.

The To Phones switch is either Mono or Stereo depending on position — you'll have to play with it to see what I mean.

Although the Mackie PROFxv3 is only stereo out over USB (even the 30 channel), it is 4 channel in. USB 3/4 are fold back channels and that can be very useful when recording.

I have one each of the 6, 10 and 12 channel versions in addition to a MOTU M4 and my AIR 192|14.

BIAB 2023 Audiophile, 24/60 Core M2 Mac Studio Ultra/8TB/192GB Sonoma, M1 MBAir, 2012 MBP
Digital Performer 11, LogicPro
Finale27.4, Dorico5, Encore5, SmartScorePro64, Notion6, Overture5