I haven't heard the NAD so I can't comment on the T757 but last year I compared Yamaha, Marantz, Denon and Anthem and the Anthem was easiest the best. This last bit I've had a Cambridge 551R and the Anthem MRX 300 in my setup and loved both units... A LOT. Cambridge has such a solid built and love the fact they shield the components inside and use a Toroidal, it sound is great very powerful and clean, very detailed and revealing its forward and kinda sharp and bright with warm edges to it keeping it from being sharp and bright, puts out a great sound stage, very transparent and 2 channel sounds amazing! Like a 2 channel amp. The things I didn't like was slow hdmi switching, no osd or EQing but SQ is great.
The Anthem is also solid built and does things different its not as bright or forward its warmer but being transparent and detailed both are musical and I find the Anthem very quick with its sound between speakers, Anthem Room Correction I found improved the sound stage and made things clearer.
The big difference I found was that the Cambridge really showed off the detail in a movie like in Avitar the girl I forget her name has beads in her hair on the Cambridge it makes sure you hear it when she turns her head and the beads clash on the Anthem it sounds more real as it doesn't make it pop as much but it sounds like it would if she turned and the beads hit naturally. The other is voices the Cambridge voices are very clear even at really low levels but it can feel like it shouting at you, there's a review on the 650R and they said it sounds like its shouting at you and I do somewhat agree with that, but its not bad it makes low volume listening great. On the Anthem voices just sound natural like how they should, its pretty cool with the Anthem as if the actor is talking near a wall or window it sounds like he's talking near a wall or a window, or in a car or tunnel or cave or whatever the vocie sounds like how it should in that environment, never heard a AVR reproduce it like this before. I prefer the Anthem for voices but I could see why many might prefer the Cambridge as its clearer and easier to hear but doesn't bring the real feeling the Anthem brings to it. Overall I found the Anthem a better movie/TV performer.
With music I would give the edge to Cambridge it sounds great here, very great, the Anthem sounds great as well but the Cambridge seemed to show flaws in the recording like you can hear echoing in the records and this is on a AppleTV so not the best source, the Anthem didn't bring that I tried to hear it but it was pretty hard to her the echoing its was very lightly there but I found with the Anthem the soundstage seemed more accurate but Cambridge would show flaws in the record which was pretty cool to hear.
I would suggest you buy both as I don't think there's a better sounding AVR then these two for this price and compare them and go with the one you like best. With the current Anthem MRX about to be replaced you could get it at a better price so you could move up a model or save more money. In the end I felt the Anthem was better for me and I'm a fan of ARC but since your 70% music I think the Cambridge will be the better unit but I would HIGHLY recommend you try both units and pick the one you like the best, also the Cambridge needs about 40 hours of break in time and yes this AVR needs it! So give it time to break in before you judge it, Athem didn't really need a break in. None of these two AVR are better than each other they have different sounds that one will prefer over the other but in all honestly I could live with either of them and be 100% happy there both really good.