i think it would be mistake to look too heavily for recurrent themes between Averse Sefira's albums - they all seem to express very distinct ideas, although they appear to do so in a certain form of allegorical sequence. each album's themes builds on those explored in the one preceding it. i find both Tetragrammatical Astygmata and Advent Parallax to be in the same caliber of quality, although i currently have a PERSONAL preference for the latter due to its more straightforwardly narrative composition.
Tetragrammatical Astygmata seems to delineate the different facets of a singular notion, a kaleidoscopic shattering of an ideal into its component parts (something that the album cover reflects) only to restructure them anew, with the final reconstruction being identical from an "objective" standpoint to the way it initially was - but new meaning is derived from that final/initial construct, as viewed through the human perception, due to being subjected to the deconstructive process. see the whole -> see the parts -> rebuild from the origins -> old tools re-emerge, but now have better implementations. it's a very "centralized" work, for lack of a better term; all things point back to (or conversely, emerge from) the center/origin/nexus.
Advent Parallax, on the other hand, seems to be a very "vectored" work; each piece leads towards the next with a heavy forward motion. instead of being kaleidoscopic, it is more prismatic - a very similar effect, but applied towards a different purpose; it is still a fracturing of light waves, only now it's been given singular direction. less reflective, but more oriented. the songs appear at first listen to simply be throwing in as many ideas as they can; and they do, but this is just the first step in a process. like the ANUS review mentions, the next is to reiterate these ideas without end until the dross is filtered out and a single unifying theme emerges from the mess. then the next batch of reiterations is thrown in. this method seems to be more prevalent in the album's first half, though; by the second, certain ideas have been chosen and are blasted out in a much more straightforward assault.
as the title suggests, the album is primarily expressive of the interplay (and inextricable bond) between two seemingly opposed concepts - dichotomy and universality. i think this explains to some degree why one might interpret the themes as being personal - in a way, they are, but in another, they are not. i've given a lot more playtime to this album than to Tetragrammatical Astygmata, so obviously i've derived more from it. sieved concepts -> implied melodies -> knowledge found through illogical means -> unity and separation are intertwined. other thoughts i've had on it:
"Recalling Brahms and Emperor, each song culminates with a formative staccato, the buildup giving new meaning to what would otherwise seem irrelevant: a return to those basic forms from which the implied melodies emerged[note: see how this ties in to the "new meaning derived from old constructs" aspect explored in the previous album]... This is accomplished by using a human approach(i.e. filter) to objectify the subjective. In other words, remove all that which is objective, see what is left, and work in opposition to it – leading to a 'para-discovery' of what is objective... In this way, a message is conveyed: the journey towards the transcendent(reality) is not only made through the experience of the mundane(human-ness), but in fact can ONLY be made through that experience... Truth is to be sought; paradoxically, it will never be achieved – the journey is what matters. Dichotomies are universal and to be embraced; unity emerges in the opposition between them, as an attractive magnetic reaction only emerges between two opposing sources brought in proximity to each other. Thus, truth only emerges from war, and stagnation is the only evil."
i don't know if this is exactly what you were looking for, but it's what i've been able to glean from Advent Parallax. if there's anything you feel i'm missing about Tetragrammatical Astygmata's expression, i'd love for you to share it. i haven't listened to that one in some time. in fact, i'm planning on getting back into it sometime this week.