Excellent beginner's guide, Craig.  A common sense approach to understanding the basics of preamps and what the various terms mean.  And very little math, yet it all makes sense.
 
 

Craig, If only you could talk them into a unit with 16 - 24 analog line inputs on 1/4" TRS...... Please!

The Focusrite 2i2 measures 46.5 volts at cable end.
The 4x4 hasn't shipped yet...

Maybe someone else could chime in with the Tascam 4x4 measurement?

My TASCAM does 46V as well. I have an early production unit, so I asked only because I wanted to make sure nothing had changed. When I first reviewed the Focusrite USB interfaces they were typically producing about +34V (FireWire ones didn't have this problem). I alerted them to this and was hoping it would be fixed, and apparently it has. Thanks for checking!

No prob "Bob"(Craig doesn't rhyme)..

charlyg
Maybe someone else could chime in with the Tascam 4x4 measurement?

https://www.youtube.com/watch?v=UkXy12xVnRs
 

Anderton
...discrete component mic pres stolen (I mean, borrowed) from TASCAM's UH-7000 interface,

 
Craig, are you saying the Ultra HDDA mic pres are one in the same as the UH-7000 (HDIA)?

Got my 4x4 today. Having an issue with Audacity not seeing it, but it seems to be fine everywhere else. latency about the same, maybe a tad better than the 2i2.

musicroom

Anderton
...discrete component mic pres stolen (I mean, borrowed) from TASCAM's UH-7000 interface,

Craig, are you saying the Ultra HDDA mic pres are one in the same as the UH-7000 (HDIA)?

I don't know if they're identical, but they sure spec out similarly and use the same technology. The main measurable difference is that the crosstalk on the UH-7000 is phenomenal. I presume this is due to circuit board layout and using separate power supplies for the left and right channels.
 
I have a UH-7000, but for me isn't wasn't better enough compared to the 4x4 to justify giving up the two extras in and the direct input for guitar.