There is a lot of confusion about the kind of cable required to get audio into an Epic or Scarlet. Let's clear that up.
One of the popular choices for XLR-to-Epic/Scarlet TRS inputs are the Hosa XVS102F. It's a 2-foot cable with a female XLR on one end and an angled 1/8" (3.5mm) TRS plug on the other. It works. Feed a balanced mic-level signal into the XLR end and you'll get good audio to your Epic/Scarley out of the TRS end.
Hosa calls this a "Stereo" cable. For our purposes, it is not. It is a cable that is capable of passing a balanced signal, and is wired to RED's spec. It works on Epic and Scarlet.
Hosa also makes a mono version of this cable, the Hosa XVM102F. It looks exactly the same, but it will not work. (Note the "M" in the part number. It stands for MONO.)
This is a wiring diagram for Hosa's XVM mono cable:
Pin 2 is wired to both the Tip and the Ring, 1 and 3 are both wired to ground (the Sleeve). This cable is not gonna work on an Epic/Scarlet.
Now, here's a wiring diagram for Hosa's XVS stereo cable:
Pins 1, 2 and 3 are are wired straight through to the proper places. This cable will work on an Epic/Scarlet.
These same principals can be applied to any other manufacturer's cables. They have to pass all three signals to their proper place: 1 to the Sleeve, 2 to the Tip, 3 to the Ring. If they don't, they will not work. Most adapter cables have a wiring diagram on the package, so you can check it out pretty easily.
I hope this helps.