Apophatic theology and Cataphatic theology in

निर्वाणषट्कम् / आत्मषट्कम्

Nirvāṇaṣaṭkam (Ātmaṣaṭkam) uses the neti neti methodology (प्रक्रिया) of Bṛhadāraṇyaka Upaniṣad. The first three lines state what the Ātmā is not. The fourth line states what Ātmā is.

मनोबुद्ध्यहंकारचित्तानि नाहं,

न च श्रोत्रजिह्वे न च घ्राणनेत्रे ।

न च व्योमभूमी न तेजो न वायुः,

चिदानन्दरूपः शिवोऽहं शिवोऽहम् ॥१॥

mano-buddhyahaṅkāra-cittāni nāhaṃ,

na ca śrotra-jihve na ca ghrāṇa-netre |
na ca vyoma-bhumī na tejo na vāyuḥ,
cidānanda-rūpaḥ śivo’haṃ śivo’ham ||1||

This presentation is comparable to Apophatic theology and Cataphatic theology in western philosophy.

i) Apophatic theology (from Ancient Greek "to deny"), aka negative theology, (Latin for "negative way" or "by way of denial"), is a theology that attempts to describe God, by negation, to speak only in terms of what may not be said about God. It stands in contrast to Cataphatic theology. - Wiki

E.g. If we compare, the neti neti expression in Bṛhadāraṇyaka Upaniṣad  2..3.6, 4.4.22 and 4.5.15, it will fall under Apophatic theology.

ii) Cataphatic theology or kataphatic theology uses "positive" terminology to describe or refer to the divine - specifically, God - i.e. terminology that describes or refers to what the divine is believed to be, in contrast to the "negative" terminology used in apophatic theology to indicate what it is believed the divine is not. - Wiki

E.g. Taittirīya Upaniṣad’s definition of Brahman as सत्यं ज्ञानमनन्तं ब्रह्म ।

(satyaṃ-jñānam-anantam brahma) - Tai.Up. 2.1 

and 

यतो वा इमानि भूतानि जायन्ते । 

येन जातानि जीवन्ति । 

यत्प्रयन्त्यभिसंविशन्ति ।

(yato vā imāni bhūtāni jāyante | 

yena jātāni jivanti | 

yat prayantyabhisaṃviśanti ) - Tai.Up. 3.1 will fall under Cataphatic theology.

There are many other statements in the Upaniṣads presenting Brahman.