I have seen nirvana described as the unborn, unconditioned, etc, but then how is it possible to experience nirvana if the experiencer is a conditioned phenomena? I feel as though there is a causal connection implied by that, which would make nirvana dependently originated and subject to permanence.
Since you said individual interpretations are ok, here is mine. I'm approaching this from a secular Buddhist perspective, one which treats Buddhism as a psychology and rejects anything unscientific.
Everything is conditioned, including Nirvana. Furthermore, since enlightenment is realizing the self is conditioned, it makes no sense to claim the enlightened "self" is unconditioned.
However, one can use "unconditioned" in a relative sense when speaking of Nirvana. Our contentment is usually a function of what we encounter, and in this we are conditioned. Yet if our contentment is relatively independent of what we encounter (Nirvana) then we can speak of us/Nirvana being unconditioned -- relatively speaking.
Again, this is to be taken in a very relative, phenomenological sense. Our biology is still conditioned, what brought us to Nirvana was conditioned, etc... Yet our experience feels unconditioned as our well-being is not dependent upon the usual conditions, and in that sense we can say we are unconditioned or that Nirvana is unconditioned.
I hope this helps.
If you are look at this problem according to a dichotomy between a subject and an object - in this case the self that perceives and a nirvana that is experienced - then you will inevitably conclude that that one conditions the other. After all, everything else we know in this world has a form that contacts the self through the sense gates and, in turn, gives rise to feelings and our thoughts about what we perceive. But what happens when we gain insight and remove that thinking subject from the equation? What happens when we gain the wisdom of non-self and directly see that everything shares in the same emptiness?
With this wisdom, the entire conditioned chain is broken. Vijja replaces avijja and action, rebirth, mind, matter, the senses, contact, feeling, birth, and all other links in the causal chain never arise. Nirvana isn't something that a "self" perceives. Nirvana is the extinction of self. It is deathless because it is never born according to the twelve links of causation. It doesn't exist "out there" in some secret place that the the mind has to discover. One doesn't find nirvana, one becomes it.
In Mahayana Chan tradition the primodial mind is called the Buddha nature. But the zen tradition also emphasises that the Buddha nature is sunyata (emptiness),the absence of an independent and substantial "self".
Hsing Yun, forty-eighth patriarch of the Linji school, equates the Buddha-nature with the dharmakāya in line with pronouncements in key tathāgatagarbha sūtras. He defines these two as:
is the inherent nature that exists in all beings. In Mahāyāna Buddhism, enlightenment is a process of uncovering this inherent nature … The Buddha nature [is] identical with transcendental reality (*nibbana). The unity of the Buddha with everything that exists.
So awakening is the mind seeing it own primordial mind, unblemished. Although they all have slightly different definitions of the Buddha nature(primordial mind). See below:
The 14th Dalai Lama, an important Gelug figure, speaking from the Madhyamaka philosophical position, sees the Buddha-nature as the "original clear light of mind", but points out that it ultimately does not exist independently, because, like all other phenomena, it is of the nature of emptiness:
Once one pronounces the words "emptiness" and "absolute", one has the impression of speaking of the same thing, in fact of the absolute. If emptiness must be explained through the use of just one of these two terms, there will be confusion. I must say this; otherwise you might think that the innate original clear light as absolute truth really exists.
Jeffrey Hopkins conveys the same understanding:
The basis of purification is the Buddha nature, which is viewed in two ways. One is the clear light nature of the mind, a positive phenomenon, and the other is the emptiness of inherent existence of the mind, a negative phenomenon, a mere absence of inherent establishment of the mind.
Germano relates Dzogchen, via Buddha-nature to Madhyamaka, Yogācāra and Abhinavagupta:
...the Great Perfection represents the most sophisticated interpretation of the so-called "Buddha nature" tradition within the context of Indo-Tibetan thought, and as such, is of extreme importance for research into classical esoteric philosophic systems such as Madhyamaka and Yogacara, while also providing fertile grounds for future explorations of the interconnections between Indo-Tibetan and East Asian forms of Buddhism, as well as between Indo-Tibetan Buddhism and contemporary Indian developments such as the tenth century non-dual Shaivism of Abhinavagupta.
The 19th/20th-century Tibetan Buddhist scholar, Shechen Gyaltsap Gyurme Pema Namgyal, sees the Buddha nature as ultimate truth, nirvana, which is constituted of profundity, primordial peace and radiance:
Buddha-nature is immaculate. It is profound, serene, unfabricated suchness, an uncompounded expanse of luminosity; nonarising, unceasing, primordial peace, spontaneously present nirvana.
As for phenomenon it is Maya - an illusion
In Mahayana... Under the influence of ignorance, we believe objects and persons to be independently real, existing apart from causes and conditions. We fail to perceive them as being empty of a real essence, whereas in fact they exist much like māyā, the magical appearance created by the magician. The magician's illusion may exist and function in the world on the basis of some props, gestures, and incantations, yet the show is illusory. The viewers participate in creating the illusion by misperceiving and drawing false conclusions. Conversely, when appearances arise and are seen as illusory, that is considered more accurate.
Altogether, there are "eight examples of illusion..: magic, a dream, a bubble, a rainbow, lightning, the moon reflected in water, a mirage, and a city of celestial musicians." Understanding that what we experience is less substantial than we believe is intended to serve the purpose of liberation from ignorance, fear, and clinging and the attainment of enlightenment..
See post of the Primordial mind of different schools