I have an older NBS Monitor iiiD digital interconnect and have been looking to invest a little in upgrading. Does anyone know how this compares to MIT Magnum Reference?
Proceed transport
Theta gen va DAC
Spectral dmc 20 preamp
Spectral dma 90

I would look into the nbs black label.  I would stay away from monitor series ( monitor series was for sacd, or music servers).. i would take the black label over the Mit cables.  
I would get the digital cable from someone who actually understands how to properly build a digital cable -  Chris Sommovigo 's Black Cat Cable springs to mind.


BTW - I had great results with Genesis Digital Lens between my Theta transport and Theta Gen Va DAC back in the days. I believe you can get one used for $300-$400 nowadays. It greatly improves the performance of the Gen Va, which is very sensitive to jitter.
Just curious why MIT cable gets no love. Found used magnum digital reference for a good price, a third of the cost of nbs black label from their discount store. 
Assamuelson... to answer your questions: mit and transparent cables are gimmick.  Believe it or not they both are related!  The network doesn't do crap, all it does is block emi and efi ( whatever that is).    You should research and see what they actually use in the network ( you will be surprise)!!  If you need me to send pixs. , just shoot me an email.    What the network does is to add more resistance and capacitance.  Imh is all b/s and snake oil!!