I am partial to NAD as a rule. The T758 is a remarkable performer. I can't say that I've auditioned any Marantz components in a couple of years, but I haven't seen anyone indicate that they have done anything to make their AVR's any better during that time frame. In my view, NAD has not dropped their signature sound, and still has a formula that outshines those mass marketed units that are OK in their own right. The reason I stay with NAD is the ability to turn up the volume to a reasonable level, and then realize that it's pretty loud. In other words, it seems that you don't have to fear turning the volume up to get a real impact out of your speakers, and then realize that it gives you listener fatigue like some of those lesser units that are mass marketed. I am always impressed with the impact you get out of a program material that isn't raspy or irritating after listening at that level for a while. A lot of these amps today are simply built to price points and sales volumes. You can't turn them up without thinking that it's too LOUD. I never get that feeling of excessive volume with the T 758, and even less so with the T 777 v3.
The way I can describe it best is that a loud passage that comes through on a crescendo or a bomb explosion in an action movie is never leaving me wanting to turn the volume down. Some other modern AVR's will have you lunging for the remote to reduce the volume. I have a couple of FIIO music players that I listen to on the T 758, and it continues to impress me every time. The proof is in the pudding, and when you hook up a NAD AVR to a decent Hi Res music player, the sound is just incredible. The proof is in the fact that I can tell the difference as to what player I am listening to. That tells me that the amplification of the program material is sufficient to being true to form. I can't say that about some of these other brands. I'm going to be straight with you (of course) and let you know that I haven't had the opportunity to review one of these mass marketed brands for a while now, but I am confident that the NAD just sounded better every time for the last 35 plus years that I've been buying NAD components.
If you could get to a place that has some auditions available, that would be the best case scenario, of course. But the fact that I have upgraded my T 758 to the T 777 v3 ( I got a great deal on the factory refurbished T777 v3) tells you that I am invested in NAD for the most obvious reason. That would be the sound signature of the NAD components. I also have a T 752 from 2003 that has a faulty display (an easy fix) that has the ability to use it's amplifiers to be used as outboard amps for later expansion (it's rated at 2 ohm usage as well) for the other NAD's I have. There was nothing at all that I could complain about with the T 758, so I put in in my MB sound system and splurged on the T 777 v3 for the video capabilities in the living room. I don't have a home theater, but I wanted to go to 4K in the future, and the T 777 v3 does that better than the T 758. I couldn't be happier. I can only make you one promise. I can promise you that you will like the sound of the T 758 v3 to the point of putting a smile on your face every time you get a chance to audition a well known song or a particular passage that you are familiar with. The T 777 v3 is simply phenomenal.
The real kicker for me is the modular upgrade ability of the NAD components. Here's the drawback though. The T 758 v3 will have upgraded cards in the future, but the price is very high on them. The pain of purchasing the upgraded cards will be less severe on the T 777 v3, as the price of the upgraded cards as a percentage will be more of an incentive to be able to hang on to the unit. A $500 card that's needed to upgrade both units will have less of a monetary hit on a $2,500 unit than a $1,300 one. It seems like a no brainer to upgrade the card on the T 777 v3 because it's 20% of the initial cost, vs the almost one third of the initial outlay for the T 758 v3. That's not a complete deal breaker though, as $500 is cheaper than $1,300 to upgrade. The T 777 v3 can be had for $1,700 as a factory refurbished unit vs $1,300 for the retail T 758 v3. A factory refurbished T 758 can be had for $1,000 (then the upgrade is a whopping 50% of initial outlay. The savings from the $2,500 retail on the T 777 v3 was substantial enough for me that I couldn't turn it down. I understand that not all folks can drop $1,800 on an AVR, and it was a lot more than I had wanted to spend, but in the end I was glad I took the plunge. The only difference is a one year vs a two year warranty.
There is just something unique about the way the NAD AVR's sound. They are capable of a a lot less listener fatigue than comparable brands. I hope I didn't hurt your hopes by introducing the option of the T 777 v3 here, but I simply had to put it out there as a somewhat viable option. I must say that the T 777 v3 is a real premium AVR that I never thought I would be able to own. You absolutely don't need it though, as the T 758 v3 is an awesome piece of kit (I'm not an Englishman, but I've always wanted to say that). Good luck in your endeavors.