here my conjecture that 5D relates to "5th dimension"
It might be worth trying to think of this matter in terms of the layout of a hotel PlatonicSkeptic.
As you may know, the C's have said there are only 7 densities and they are like the core, integrated fabric of the central purpose of the universal whole. These different vibrational arenas are like the floors on a hotel starting at the basement (a bit grim and sparse) moving up via lifts all the way to the 7th floor (where lets say there is a glorious, light filled, unimaginably beautiful penthouse). These 7 floors provide fundamentally different landscapes or environments for those who spend time in them and are populated by different levels of consciousness at different levels of awareness and being. All 7 are 'vibrationally' different from each other. In some utterly mysterious way it is rumored that Floor 7 contains the unified essence of all that exists in floors 1-6! But that's beyond me!
Floors 1-4 share certain key things in common but as you go up the hard and fast form of it gradually dilutes into a more 'airy', what we might call 'magical' or 'etherial' quality. All the inhabitants of these floors can go to Floor 5 every once in a while for a sauna and a scrub down but they must then return to whatever floor below suits where they are in terms of the purpose of their stay (their consciousness and awareness). Floor 6 is near invisible to these inhabitants until they are fully ready to see it because on their terms it maybe doesn't 'exist' - as they are as yet not ready to inhabit its totally 'ethereal' (pure thought-form) reality. As for level 7... well it is known to exist but no one has met anyone whose been there...
On each corridor of each floor, however, are doors that go through into different rooms and each room is decorated differently albeit on a theme that relates to the nature of the floor one is on. Two rooms can be right next to each other but when you enter they appear to be very different worlds or 'dimensions' and there is no apparent connection to the room right next door (though from time to time, mysteriously, an interlocking door might appear in the walls between them - and this can cause surprises for the guests on either side of this normal divide!) One room might be purple with soft gentle furnishings, another room next door all dark and disturbing with a bed on the ceiling! Yet they are all part of that particular floor and its 'strengths' and 'weaknesses' - its underlying totality of rules - come what may - and they can only in some way reflect and obey these rules of that particular density floor.
Do you see the difference? Yes the rooms appear to be a world unto themselves but they still reside on and abide by the governing limitations and scope of the floor of the hotel they are on. And their occupants know no more about the floors and rooms above than they may know about those below... or even next door (though lets just posit that you only get to move up a floor when you have at some level digested the 'lessons' of the entire floor though not necessarily needing to spend time in that many rooms - maybe no more than one - to do so).
When you have learned the lessons of that floor you are ready to move up to the next - and inhabit whatever room/dimension fits your purpose of being on that floor/density (good to remember that 3rd Density earth is perhaps also just one room or 'dimension' of many, many forms of possibility on the 3rd floor).
I share this overly simplistic analogy/thought picture with you to suggest it might be worth thinking on this for a while because you do appear determined to keep hold of your idea that dimensions and densities are interchangeable and I would suggest that such an approach may only lead you to a number of confusions that perhaps won't serve you in the long term. FWIW.