Sounds like a tough choice!
I'm using a Squeezebox Touch with TT3.0, EDO (USB output up to 192KHz) and TeraDak PSU as a digital source, digital cable is an Apogee Wyde Eye.
The price difference is enormous - I can get around €600 for my Octave but I'll have to buy the Master 7 brand new which costs €2155.
Spending €1555 for a side-grade isn't the most brilliant idea ;)
Also the offramp is another $1200, that's a no go. Way out of my budget.
By the way, what about the Sabre based NFB-7?
My goal is extreme resolution in the mid and high range and tight bass (I run a bi-amped JBL hybrid-4343)
The Octave is nice but the mid is a bit pushed forward to my taste, also I miss some sprakle in the highs (NOS?).
I won't debate that I2S isn't the ultimate way to go with this dac because it is, but for a while I used the $99 Schiit Wyrd straight into the M7 usb latest version and it was fantastic.