I was just playing with Re-Wire and accidentally installed another set of ASIO drivers which caused me to delete that software. As I was setting up things again, there is now an "ASIO Saffire Pro 24 Loop 1" input driver which I swear did not exist before (anyone know if this is new to MixControl 3.4, or did I just miss it before???).
 
Long story short... with MixControl 3.4, whatever signal is assigned to LoopBack (mix of your choice) is sent to this input driver, so is very simple to create an audio track, select "Loop 1" as the input and record "what you hear" like in the days of old. No physical loopback cabling required (yay Focusrite... I love those guys!).
 
This came to mind from this thread, but I wanted to throw this out for folks. I am sure other interfaces have similar features and know that it could be done previously with the Saffire 24, but a feedback loop was a serious issue (many warnings in the Saffire manual on this too)... apparently this input driver is to streamline routing, and a quick test of this works like a charm.

My Saffire Pro 40 had this since the day I bought it, or at least I think so... So, you probably missed it :)
I've used it a couple years ago, so I'm sure it was there before 3.4.
 

It is quite possible I disabled this, but I thought I had only disabled SPDIF/ADAT channels. I am glad this happened to me, since I read the manual a couple times which doesn't give focus to this important detail (although it mentioned the loopback routing, I didn't catch the "Loop 1" input). Since I run Windows sounds on my RealTek, I rarely shift the computer "as a whole" to the Saffire. What didn't make sense until I actually did this is "DAW 1/2" is actually the Saffire "main outs" as far as that "Loop 1" input is concerned.
 
For those interested, the "quick and dirty" way to use this is to:

1. Have Windows sounds run through the Saffire.
2. Loopback DAW 1/2 in the router settings (to record "What you Hear"). Modify DAW 1/2 to a mix if preferred for more versatility.
3. Create an audio track with Saffire Loop1 as the input. When recording, I muted the recording track to prevent feedback from it.

I really wish I had realized it was this simple a year ago. Realizing this got 3 more cables off my desk (yay).

Saffire Pro capability.  For those of us with Saffire Scarletts we don't have that loopback feature unfortunately.

Hold the phone... I just checked quick and Focusrite's own tutorial only calls out "Saffire" as well. I am very confused now why this would only apply to the FireWire interfaces.
 
https://www.youtube.com/watch?v=iHB23zs-0l0
 
I guess I need to update the title, I am sorry.