Is my amp good enough?

I think the point many are trying to make is that you may want to go up the chain in terms of sound quality once you have had the speakers for a bit. Trust me, watts are not just watts, both amps and preamps make a big difference. There was always some degree of graininess in the sound of my earlier system, I have eliminated that through upgrades. 

Absolutely. Something I will no doubt consider down the road.

@neversatisfied 

The NAD 375BEE spits out 410 Watts into a 4 Ohm speaker. The Golds, at 4 Ohm, are rated at 250W RMS. (Think of 250W RMS as the average power your speakers will be given at any time). So together they are a good match with regard to specifications. 

Marrying up separates (varying manufacturers) can be daunting as making mistakes with your money can cause second thoughts and buyers remorse. But buying a set of new speakers that is highly rated is not really one of them. They are, after all, in the range of where you need to be in order to fill out your system with similar costing gear and they are highly rated with excellent feedback from other owners.

With relation to your intentions, your pre-amp, amp, source, and speakers should be in the 1K range with regards to price. If each speaker comes in around 1K each, that is a good fit for your overall plan of monetary attack. If you spend more on any one than the other - make it the source. A great DAC or Turntable will do more for your system sound (it's the starting point!) than any other component. 

It is reasonable that your current setup sounds a bit "thin". (I started my trek with the NAD 375BEE (with an NAD front end) and figure you are probably hearing what I heard many years ago). You likely only use a fraction of the watts of the amp (probably don't go past 10 o'clock on the volume dial in a listening session). So, a better set of speakers will push your amp to do more, which will end up creating "body" with regards to your sound. Think thick over thin. One surefire way to gauge this is to listen to your current speakers for a couple of hours and touch your amp afterwards. It will likely be warm. After installing your new speakers, and listening for the same amount of time, your amp will likely be much warmer to the touch - perhaps even hot - depending on the volume levels you are providing. This is proof that you have succeeded in making your gear work for you, or pushing it to the limits of what is is capable of doing. 

As others have said, another way to push your amp to do more for you would be to install sound dampening/baffles behind your speaker (and elsewhere) which again, allow you to be more aggressive with turning up the sound. Your amp should be working hard for you, but your speakers should be doing the same. Everyone here can agree that sound dampening enforces bass, which is another tool in the fight against a thin sound. Since you are forking out a couple grand, you should be asking the sales person to move the speakers you are buying around the showroom floor to understand how it works best in relation to your own room, as whatever dampening/distance from walls your speakers need in the store will be similar in regards to your own listening room.

First of all, if you are truly satisfied, don't waste time and money. I suspect that you really are not satisfied. If correct, the question is why is it that you are not satisfied.

I.M.O., if you are not experiencing listening fatigue, then you are wasting your money. If you are experiencing listening fatigue, you need to figure out what's bothering you.

Some are hyper sensitive to phase and time alignment. Some are concerned with hearing obscure details. If details are a big problem you may want to stick to monitors as they have less bass making details more readily audible. Then again some want details but also want bass. Some want "warm" systems, systems lacking in details. For them details are akin to brightness, even though it's really not bright. I know a guy who has serious high frequency hearing loss. To him a system that would send most out of the room holding their ears is awesome.

Music is personal. You like what you like, but you need to figure out what that is or you can spend many thousands and still be unhappy with your system.

If you want to seriously replicate a life like experience you're in big trouble. You need have a big pile of money. You can minimize the money somewhat if you can solder, or have a friend who can.

I am a detail, be there type. Open baffle is the ideal, but full range planer type speakers physically tend to have limited dynamics. Used Spatial Audio Saphire S speakers are supposed to be quite good, that's hearsay multiplied because I have not personally heard them. Perhaps the biggest problem will be finding neutral electronics, cables, etc.

if time and phase are critical to you Thiel, and Vandersteens are a good starting point. Unfortunately Thiel is only available used, and I have not heard the newest Vandersteens, the older ones are quite warm. I'm not sure that you could even hear cable differences with the older Vandersteens. The new ones are at least much better, but the system was less than ideal so I can't say if you can get details and phase/time alignment with them.

Personally while phase alignment is doable, I consider time alignment somewhat of a canard because it will only be correctly aligned at a specific distance, and your room may not allow for that.

IMO, the smart money is saving up to spend the most you are willing to pay for equipment regardless of your preferences. Otherwise you'll end up incrementally buying amp after amp for instance usually loosing money all the while.

Had I knuckled down and purchased a M.L. 27.5 decades ago, I would have ultimately spent a lot once, but far less over time on amplifiers. Today there are far more neutral, my preference, than just one or two. Even older good amps are expensive, and replacing their electrolytic capacitors is a good idea yet further increases the cost of older gear.

So, I doubt that I have resolved your issues, but hopefully I have told you something that you can find value in.

So I just came back from the audition. They used the lowest Arcam model available which the salesman said would be comparable to my  amp. 
 

Absolutely amazing! I was totally blown away with how much better they sound vs my 20 year old Silver 10’s. It was immediately apparent. We listened to a good range of music styles to cover all the bases. He moved the speakers to where the amp was setup and I guess as it was not the highest end amp in the place, it was not in an ideal setting for room treatment. And yet still the speakers were outstanding.

I have no fear that they will not sound awe inspiring in my listening room here at home. I plunked down my Visa card without hesitation. The local warehouse was out of stock here in Canada so I am waiting for a shipment from the States. Should be a couple of weeks. I can’t wait.

Congrats !!!!