Well that's the thing that confuses me, because using them interchangeablly they are sort of mixing western and eastern concepts.
The Abyss would be like Tartarus, but like you said, it's just a part of Hades. So I'm thinking this "raw" fade is still technically part of the fade, but makes up the lower layers or realms, close to the Void. There is still some light and energy there.
The Void would then be something more like the Tao, it's a constant, and it may be where the Black City is, which can be seen from any point in the center of the fade.
Like the Golden City is associated with the Maker and solar imagery in the lore, and with masculine principles, like gold, light, fire, electricity, dryness, warmth, etc....the The black city could be the corresponding polarity of that. Coldness, water, wetness, magnetism, etc. The void is often given feminine imagery, like that of an egg or womb, and personified as a female dragon, or spider.
If I recall correctly, the Chantry believes in the Void existing in all things (in the Fade, in the world, in people and beings), on one hand it sounds like limbo between the world & the Fade, on the other hand it exists in both so that's.. weird. It kind of sounds like 'gaps' in everything that exists.
I'm not sure if the Chantry sees the abyss as the Void, I think that when they speak about the abyss they mean the Fade?
Elves seem to indeed use the term interchangeably, and I think for them it's a physical place, under the ground.
I think that perhaps 'abyss' is what it is and the 'Void' is sort of contained within, or part of the 'abyss' (like the deepest part of it)
In the comics Aurelian Titus says "there are void places, gaps between the dreams" probably referring to the raw Fade. I believe he used the word 'void' just to describe said gaps and I don't think it says something about "the Void" or "the abyss".
I tend to go with the elven interpretation of the Void/abyss and imagine the world like this
Waking world (home of all creatures)
Void -> Abyss (Forgotten Ones), Titans, Thedas
-----
Veil
-----
Dream world (home of spirits)
[Raw] Fade, Golden/Black city (Evanuris)
Pre-Veil the waking world was affected by the Fade and (perhaps) by the Titans and vice versa, the Fade was always around but only truly visible for spirits (so it could only be truly explored by the elves while sleeping, when their spirits were free from the constraints of their bodies). There was balance between the Fade & the world that allowed physical structures to levitate but at the same time prevented fire from flowing like water.
Post-Veil that balance was ruined, the Veil went up, pushing the energy of Fade back, cutting people from the Fade (making it mages in the long run a lot more rare and making exploration of the Fade near impossible for most), making buildings fall from the sky.
My guess is that the Evanuri found a way to walk through the raw Fade (the same way Kieran did) and built a palace there, because the palace is the only inorganic thing in the Fade the spirits cannot change it and so it's always there, in the center of the Fade.
As far as I imagine the abyss I kind of think about a different version of the "hollow earth" hypothesis
The fact that inside the titan you have sun and clouds makes it fit even more, I imagine something like Thedas up above, Titans below "pillars of the earth" if you will and in the middle the Void.
The story about Elgar'nan throwing the 'sun' into the abyss sits really well with me because of that XP