I don’t know if this will help, but I thought I would share my set-up with you.
I have five Naim boxes: NDX 2/XPS DR, NAC252/SuperCap DR, NAP 250 DR (as well as a blu-ray player and a headphone amplifier).
My room is long and rectangular, so rather than put my two racks beside each other I put the one with the brawn behind the one with the brain. This makes cable management much easier. Also, I get a better soundstage without a large stack of boxes between my speakers.
I have never understood why so many people put their racks so tight against the wall.
Personally I would reverse the 252 and NDX, but that’s how I had it when I had that exact system of six boxes (but on brain/brawn). When I had eight boxes it was (top down) 252 - SuperLine - NDX2 - 300
To make things even more complicated, the Fraim’s toughened glass sub-shelf has a top that rings like a tuning fork (Ding!) and a bottom that does not ring (donk.).
I learned this tweak earlier this year on this forum.
My preferred set-up is the 252 on top with a glass sub-shelf that Dings! and the NDX 2 on the second shelf on a glass sub-shelf that does not ring (donk.).
I’d go with the suggestion above. I use that myself in a single stack albeit with a 552 rather than a 252. It seems to work well but it may be worth you trying the 252 on top as it does have a reputation for being a little fussier over placement.
You say you have 7 shelves, but it seems that you only need 6, which is good, as Naim don’t recommend very tall stacks of Fraim. On the other hand, cable dressing on a single stack can be tricky, and having a bit of extra space between boxes can help with this, as well as putting some distance between the brain and brawn sections of your system. So if you want to use the full stack it could have some advantages.
As already mentioned above: try the preamp on top rather than the streamer.
I have very similar system and after a lot of trial end error and reading what other people have, I ended up with:
252
NDX2
300DR
SCDR
555PS
300PS
Obviously, this keeps the ‘brawn’ on the bottom three shelves and the ‘brains; on the top three. So first objective met.
The reason for the order then is to ease cable dressing - in this configuration you have the same number of shelves between each component and it’s PSU. So having it like this eases cable dressing and it’s possible to ensure that burndy cables are not touching each other, or the floor, and are dressed optimally.
I’ve gone to the effort of de-stressing or ‘relaxing’ the burndys and other signal cables and this makes far more difference than I could have ever imagined.
There seems to be a lot of debate as to whether the source or preamp should go at the top and nothing conclusive, so my preference is to have the amp at the top.