Now, I'm confused.

"I doubt changing the preamp will give you a wider so"
over 2000 posts and you are still giving dubious advice? yeesh. the type of preamp a person uses and whether is uses SS vs tube is a well-supported concept, with literally thousands of pages of forums delving into this concept.

The Saga would be a good start, it has tubes which is well-known for giving a either a larger soundstage, or at the least "sounding" like a larger soundstage. Let me explain.

There is a concept in audio that certain electronic devices give off different types of distortion: higher order harmonics (a type of distortion) versus lower order harmonics (distortion). the tube distortion is, to me and many others, the preferable type of distortion, b/c it doesn’t hurt your ears as much as from the SS, AND b/c it exudes a sonic "presence", meaning that tubes will often exude a wider and deeper sense of space ... IOWs = soundstage.

I’ve used tubes for 10 years, and I’ve been in your position. The Saga is good, but it only has one 6sn7 tube. Its a great tube, and it will provide an audible difference in soundstage I believe. But it is only a smaller change. I would encourage you to get a PreAmp with 2 tubes for the more significant soundstage that you are after.

for example, I have and use the Schiit Lyr 2. It is both a preamp and headphone/HP amp. it has 2 tubes (ECC88 type which will take a few different types of tubes: 6922, 6dJ8, etc). The Lyra 2 is listed under HPs on the Schiit site. The preamp section is intended for smaller desktop systems, and has a hi/lo gain. I use it will a full-sized bookshelf system with a pair of tube monoblocks I built and a pair of Zu Omens. It sounds fantastic, and I change the hi/lo gain depending on the source (LP vs DAC, etc) and the recording. modern recordings are fine on low gain. older recordings (70s) often need higher gain. (the Lyr only has 1 input, so you may want to get an external device with more inputs, Schiit makes one in fact, but only allows 2 ins, but there are very good options out there)

The Freya would be great: it has 4 6sn7 tubes and all the tube/ss/passive options. if you dont need the XLRs, dont worry, just dont use them. It is an unbelievable price for what the Freya offers.

IOWs, you can get a used Lyr2 for the price of a new Saga. And you can get a used Freya for the price of a new Lyr 2.
I would say, just go for it. you have a good supportive system and great Vandersteens! one of the best selling audiophile speakers of all time

no Geoff, not wrong, just reality-based.
Soundstage can be improved with many things, as stated above, from the Dual to the cartridge, to the phono stage to the cables, to his amps. But this guy just wants to make one or two simple upgrades.
(and I cant suggest Morrow, based on my prior experience with them and their cables). 

Dude, your system is fine. Suggest that you do what most of us do, replace one piece of equipment at a time. Save your money, and a few months down the road, replace another piece of equipment. And on and on. that is the great thing about this hobby, it will continue to grow and change for the better over time. that is where the fun is!

But it is true that the source has to be a good quality to keep good sound quality from source to speakers. SQ only degrades from source to speakers, it does NOT improve along the way. it will change, yes, but you cant recover resolution after you have lost it.

However, the Schiit tubed preamps you are looking at do NOT have a built-in phono stage like the NAD 162, so if you swapped your preamp, then you would still have to have a phono stage. Tubed preamps with built-in phono stages tend to get expensive quickly. 

And generally speaking, phono stages built into preAmps tend to be of lower quality. Even though the NAD 162 is a perfectly capable preamp, the phono stage probably is not that well supported, more of an accessory, and likely part of the reason you are not getting the soundstage you want, as posted above.

IMO/IME, the cheapest route to get what you want would probably be a SS external phono stage running into a small tubed preamp. That will make a very noticeable difference in your sound quality AND soundstage. 

I would suggest the German made Clear Audio mini phone stage. I have one myself for 3-4 years now. Before I bought it, I walked into an AV store in San francisco and asked the TT/Turntable guy, "Which phono stage would you recommend for around $500? The Clear Audio Nano v2, he said. Then I asked him, which phono stage he would suggest for $500-$1000? ..... The Clear Audio Nano v2 he said, the same one he said before. !

The Clear Audio Nano V2 is here: http://clearaudio.de/en/products/electronics-nano_phono_v2.php
it runs MM and MC, can specify some filters like subsonic, etc.
New = $500, used = $250. 

And to reconsider, perhaps getting a better phono stage would be your first buy. Run the Dual into the Clear Audio and then into the inputs of the NAD 162, then add the tube preamp which will put a smile on your face.
good luck

I can appreciate all the suggestions for room treatments, but isn't that like putting lipstick on a pig?

I mean, room affects sound/stage, but wouldn't a person want to start with the equipment first?

And room treatments, at least good ones, are very expensive. Look at the OPs list of gear, I dont see that the GIK stuff is similar in pricing. I mean, suggesting one GIK would cost more than his preamplifier or other piece of equipment. IOWs, it does not make sense to me. Yes, the room traps/diffusers will help him, but at what price? and then he never figures out which parts of his audio chain hinder the soundstage.