I was considering those exact same three units, the Lexicon RV-6, the Anthem, and the NAD T778. I went with the NAD b/c Dirac, because it looked better, and because BluOS will play high-rez files from Amazon Premium Music, and because of good online reviews about sound quality.
Have fun when you get your T778. I can help you skip some initial frustration:
First let me tell you how to set up wireless so you don't go nuts trying to find it in the menus or in the manual. The manual only teases you about it. ("See section below on wireless." Then there is no such section.) You would expect a network option in the setup menu, but there is no such thing.
Download the BluOS app to your phone or tablet. Your T778 will come with a wireless "dongle" that needs to be plugged into the rear USB jack. Be sure to use the included USB extender so the dongle is not right up against the rear of the unit. Power up the dongled T778 and open the BluOS app on your phone. The app should find the T778, and the first thing it will tell you is that the T778 needs to be hooked up to wifi. Use your app to tell it the network and password for the wifi. Basically it's the exact same process you use to connect Alexa to your home network.
Once that is done, you can upgrade the firmware over wifi.
Now get all your inputs and speakers hooked up the way you like, label your inputs in the menu, etc. I found it easiest to just use the touch screen menu on the front of the device to label and set the parameters for the inputs.
Once it's all set up how you want it, you can download the Dirac Live app to your phone or PC and proceed to do the room correction. I had really bad luck trying to do it over wifi with my phone, however. Wasted a whole evening getting error messages. The next day I brought home a 60 foot ethernet cable from work and plugged the NAD into my home router, and downloaded the Dirac Live for Windows to my desktop. This time Dirac worked like a charm with zero error messages. There are more functions in the desktop version of Dirac than the mobile app.
The remote control is also not very intuitive. It took me forever to figure out that the numbers are how you change the input you want to hear. Also, if you have a Dirac curve profile loaded, the unit will not let you manually adjust the speaker levels for Front R and L.
So far, so good. Have fun!