Ivan, regarding SMAART interfaces, the UMC404 has been replaced by a newer version UMC404HD. Pretty cheap at $99 for 4 mic preamps and the XLR outs are a bonus. It has global phantom.
Have you ever had a problem with global phantom and looping back your reference from/to your UMC202? I had a problem years ago with an Edirol interface where the phantom power messed up the loopback signal.
Lately I've been using my GLD as a SMAART interface, but I'm starting to work on other people's systems more frequently and need at least 4 portable channels. $99 is pretty much a no-brainer investment.
My standard cable that I use for dual transfer functions has a TRS on one end-but only hooked up to the T and S.
There are 2 cables that come out of the connector.
The connector plugs into the headphone output.
One is a TRS-with the hot to tip and the shield to R (no connection to shield)
This goes to the TRS input of the reference channel
The other cable is a MXLR that has the tip hooked to pin2 and the shield hooked to pin 3.
This allows me to vary the SPL out of the loudspeaker, without affecting the signal displayed-since both the reference and measurement go up and down at the same time.
It is also REAL good for looking at power compression of drivers in real time.