This might, in fact, be a moot question and it has already been discussed and argued at length here on the forum. But just for the sake of it and to see if it is, in fact, moot I’ll ask it regardless.
How good is the NSC222 without an extra power supply?
This topic is triggered by a Naim dealer claiming it is way better than NDS/555DR with NAC82.
And I know I have to listen for myself in my home and system.
So let’s see. Is it moot?
Why don’t you ask him to set up a demo to show exactly how those two systems compare? Then you can come back and tell us what a bullshitter he is.
It’s a bit like asking whether blue is better than red. It totally depends on whether you prefer blue or red. Your dealer has given you their honest preference. I know a dealer who prefers the old classic range over the New Classic, of which they are not convinced about the superiority at all. Again, a personal preference.
Like many of us, I understand a pre-purchase demonstration might be difficult depending on location, but if you can, that would be the only way to answer the question. Sound quality is, at least at the level we are talking about, not a fact but an opinion.
As was said, he should be lining up a demo so you can hear for yourself the comparison. Else, why even make such a claim if he isn’t willing to demonstrate. Edit - removed first comment, just noticed you’re running the set up the dealer is referencing.
I wish I could but he is a 12 hour drive from were I live😅
Yes I sort of had a feeling this topic was a moot.
That would be a dream scenario but very difficult to execute.
Perhaps said dealer doesn’t have a NDS or a NAC82 that he can sell you for a good profit…
Perhaps he would be happy to send the NSC 222 / NAP 250 system to you to evaluate at home? A dealer demo won’t tell you if the system works well in your room at home.
Whilst I’ve not heard a system like yours, I would imagine they will mainly sound different - so it will be down to your preference.
Probably not but I asked him about his opinion only and was transparent about the fact that I am looking at a used NSC222 so he wasn’t pushing to sell anything to me.
However I think he and I have a very different view om what is ”good” sound because I also asked him if he thought the NDX 2 was better than NDS and he thought even the ND5xs2 was on par with NDS. I haven’t heard the ND5xs2 or the NDX but have never heard anyone say the ND5xs2 being on par with NDS.
Yes he probably would. However I asked him without the intention of buying from him. I bought my NDS from him and wanted his view because I’m looking at a used NSC222
But I’m assuming you wouldn’t need to buy it to do the home demo. Although it would be a bit cheeky to ask him given that he knows you are looking for used. His risk though.
I know @Dan_M does not agree 
And I’ve had NDX2+555PSDR in head to head with NDS+555PSDR and kept NDS even though it is more of a fight in compatibility.
Do people generally believe what dealers tell them? I have visited only two dealers in the last few years, one is predominantly a Linn dealer but sells other brands including Naim. He has heard the Statement and nap500 power amps and doesn’t rate them saying “What’s wrong with the 300?”. The other sells mainly Accuphase but stocks Naim. He hasn’t sold any Naim kit for 2years and is dropping the brand. Even the advice on this forum can go from one extreme to the other. Listening to many varying views over a long period of time and using my own gut feel is what I tend to do. Regardless of how honest or experienced a dealer is, they are only giving you their view. Trust your feelings Luke 
Yes I know and thought of your experience when he told me his view
Yes a bit cheeky. But as you say, his risk.
Sorry, but that is complete and utter bullshit. Nobody who had heard the two would ever say that. Sounds to me like he is just talking up the products he might be able to sell.
Yes it just goes to show how different our views and perspectives really are. And that in it self is quite interesting. I mean not all things in life are subjective. Some things are objectively better than others. With hifi less so, it seems. Someone equals ND5xs2 to NDS/555 and others find the preamp in NSC222 to be above that of the 252 while others have the opposite view. How we can understand each other regarding these questions is a complete mystery to me. It probably mirrors other things in life as well though.
Yes I have a very hard time believing that would be the case.
Have you considered asking the dealer about what deal might be possible. If their ex dem price could be brought to nearer a used price, it would make sense to have it couriered on a sale or return basis. I think it would be wrong to borrow it if you don’t intend to buy from them. It would be scummy and underhand.
Is this a plan to simplify things and get the latest functionality? If so, the 222 could make sense even if it’s not technically as good as your NDS. Would you plan to keep the 555? If so you’d need to buy special leads to connect it to the 222, and you’d also need leads to connect to your 250 as your din to XLR won’t work.
When I had a 272/555 I pondered about an NDS and was gently steered away from it as the difference wouldn’t be much. So I’d expect a 222/555 to be even closer.