Stacking your system on top of each other is a bad move. You will damage your units cosmetically and won’t get the best out of them.
This is why I would recommend a Fraim support system or other shelving system.
The marks from stacking will degrade the cases leaving marks, leading to poorer resale values.
At the very least use pads or small bits of card to avoid marking the units.
Naim units are designed to be separated to get the best from your system
Yes. Use the ND5XS2 as your streamer and 272 as a preamp.
+1 for using the 272 as a preamp. I used it with an HDX and NDAC. Sounded great, particularly with the extra PS on the 272. The 272 is terrific value as a preamp and you get that cool digital volume control!
The 272 preamp is regarded by most as about as good as 82 or 282.
I have ND5XS2/82/HC/250 in one system and it is excellent.
If a matching 250 is simply too expensive, you could get a (serviced) olive 250.
Adding those together…
ND5XS2 will give be a better streaming source and you get current architecture and Qobuz etc. A s/h ND5XS2 and an older 250 would be great with a 272 as the preamp but you will also want to find somewhere to put a PS for the 272.
Good luck!
While the nd5xs2 is a very competent streamer/dac, I would avoid using it with a 282. It will sound good, engaging and fun on a 282, but you won’t be able to hear how good the 282 is. IME the 282 really needs a better source to shine, a nDAC, for example, or ndx2.
A nd5xs2 into 202/200 (or SN2/SN3) would be a more balanced system, and will give you recent streaming technologies.
You could also use the nd5xs2 in a 272/200 system. Not sure the 272 is closer to 282 than a 202.
My understanding is a 272 shines with an XPSDR and better still with a 555PSDR.
A 272 555PSDR 300DR was quite popular a few years back.
@GlenJ is right imho that NDX2 is better than ND5XS2 and that adding nDAC to ND5XS2 is another good way to get that extra SQ.
However, when we tried, it really took a 52 to show the difference -the ND5XS2 was very good and not dramatically inferior when using an 82, at least to my old ears. As you can see, others hear it differently.
I am sure @Dan_M is also right that adding XPSDR to a 272 is a big improvement (and very much warranted given what else you are considering). He is definitely right that a 300DR is a great amp - well ahead of a 250, and that a 555PSDR improves over XPSDR in pretty much any application.
Sadly, we are all happily spending ever-increasing amounts of @Tappy ’s money, and making a simple system a good deal bigger….
Yes, but it will be magnificent! 
Trying to find a 555 is the challenge though. People hang on to them
NAC272 is almost at 282 level. Tempted to use it just as a preamp with a power supply
Have you ever tested that in person Nick? I have, tried my (then) CDS3 into a 272 as an alternative to my 282 because I liked the idea of a streamer, not a chance 282 way better.
With what power supply Lindsay, it’s not clear from your post?
FWIW a 272/XPS2 replaced my 282/HC2. It was a big step on from my prev streaming and more convenient. With the P9 it wasn’t as good, but it was a compromise I was willing to make.
I don’t think I’d make the same decision again. Streaming quality has moved on quite a bit.
We started naked and then added the XPS which at the time I had on my CDS3, with and without similar to your experience with your Rega it just didn’t cut the mustard. Around the time I also went to a demo at a well renowned dealer who compared NDX2/SN3 vs 272/250 with Sopra 2ss and with one exception all in the room agreed that the former was considerably better. But of course all comes down to personal preference.
I own both and have tested both. The 282 is better, and the more you add to it the better it gets, but my comparison is not between a 282/ND5SX2/ Hicap and a naked 272/200…it’s between the 272/200 vs a 202/200/ND5SX2 and the 272/200 wins hands down which surprised me.
I love my 282 and it’s soon to be paired with a near new NDX2 and non-Naim PS.
The 272/200 vs 202/200/ND5XS2 is my quandary for my home office. First world problems I know but really appearing everyone’s perspective and input so thank you all 
For me, separates win every time on sound quality when I’ve compared them. If convenience is a priority in a second system I think the 272 still has its place, though. Fewer boxes and cables, better volume control.
I would also consider NDX2/Supernait if you want simplicity, or even ND5XS2/Supernait, in preference to a 272, but if you don’t mind the extra boxes, again I would go for separate pre/power amp every time.