आगमे शैवे विश्वासटिप्पन्यः

(Source: https://threader.app/thread/1445246256423620610)

There is this tantalizing fragment from the nishvAsaguhya where where nandin is explaining the pa~nchabrahma as per the vaimala & saiddhAntika tradition to a v1 interlocutor

पञ्च-मन्त्रमयं देवं पञ्च-मन्त्र-शरीरिणम्।
पञ्चमन्त्र … मन्त्र … सदाशिवम् ||

Unfortunately there are lacunae in the text & the next sentence is mostly lost but it seems to describe shiva’s form as made up of the 5-brahma-s. nandin clearly lays out the objectives of the deployment of 5:

दीक्षा ज्ञानं च चर्या च
मन्त्र-भूति-विनिर्णयः।
मन्त्र-भूतार्थ-चर्या च
रुद्र-सायोज्य-गामिनी॥

Note: mantra-bhUti-vinirNaya: ascertaining the power of the mantra & and mantra-bhUtArtha-charyA: the practice of their actualization; the final objective is oneness with rudra.

A lost lAkula text explains that oneness with rudra thus:

आकृतिम् अपि परिहृत्य
ध्यानं नित्यं परे रुद्रे ।
येन प्राप्तं योगे मुहूर्तम्
अपि तत् परो योगः ॥

The yoga by which the constant meditation in the primal rudra is established even for a muhUrta is the highest yoga.

There are some points of note here:

if the the yoga can be established for just a muhUrta then how can it be nityam? Hence, nityam should be interpreted as constant -i.e. unbroken dhyAna for a muhUrta.
If the primal rudra is आकृतिम् अपि परिहृत्य - even though devoid of form then how can anyone attain dhyAna -i.e. visualization. Here is where early atimArga emphasizes something special: “a first person direct experience of rudra” – dhyAna which can happen without the objective visualization of a rudra with a form.

This continues via the bhairavasrotas in mantramArgaThe early saiddhAntika-s saw themselves as superseding successive layers of pAshupata-s hierarchically associated them with the heads of rudra:

ईशाने शैवम् उत्पन्नं
वैमलं पुरुषात् स्मृतम् ।
प्रमाणं हृदयाज् जातं
वामदेवात् तु कारुकम् ॥

From the IshAna head arose shaiva (siddhAnta)
the vaimala arose from tatpuruSha;
the pramANa arose from the heart mantra (=aghora);
the kAruka (=old kAruSha, a student of lakula at mathurA) from vAmadeva.

सद्याच् च लकुलीशान्तः पञ्चभेदाः प्रकीर्तिताः ।
from sadyojAta rose the lakula; these are known as the 5 textual divisions

ब्रह्म-विष्णु-सुराः सर्वे
गणाः स्कन्द-पुरोगमाः ।
ऋषयो ऽप्सरसो यक्षा
नाग-गन्धर्व-किन्नराः ॥
दैत्या विद्याधरा सर्वे
ये चान्ये पुर-वासिनः ।
स्थाप्य पञ्च-तनुं देवम्
अर्चयन्ति सदाशिवम् ॥

brahman, viShNu, all the gods, the gaNa-s led by skanda, the seers, apsaras-es, yakSha-s, snakes,gandharva-s, kinnara-s, daitya-s, vidyAdhara-s all these and others dwelling in the fort [of rudra] having installed the five-formed god caused sadAshiva [the supreme deity of siddhAnta] to be worshiped.

I speculatively but not without basis interpret the 2 pa~nchAkSharI-s of the pramANa tradition of the atimArga as meditations of the highest rudra-s in the sun and the Polestar: ॐ तेजीश नमः ।ॐ ध्रुवेश नमः । respectively.