Sri Ayyanna Dikshitar, in his 'Vyasa Tatparya Nirnaya', says that Shankara Bhagavatpada had based his bhashya on the Suta Samhita (a part of the Skanda Purana). Swami Vidyaranya too has cited from this text in his Jivanmukti Viveka.
A citation from this text in the commentary to the Viveka chudamani (426) by HH Sri Chandrashekhara Bharati Mahaswamin seems to give credence to the above belief:
सोऽश्नुते सकलान् कामान् अक्रमेण सुरर्षभाः |
विदितब्रह्मरूपेण जीवन्मुक्तो न संशयः ||
The Jnani upon realizing his non-difference from Brahman, experiences the entirety of bhoga, joy. He does this not sequentially but simultaneously.
The above verse is found in the Sutasamhita - Brahmagita section where several Upanishads, including the Kaivalya, have been condensed in verse form:
What is interesting in the above verse is: the idea that the Brahmavit experiences all the joys in one go and not sequentially. This is exactly what Shankara says in the Taittiriya Upanishad bhashya:
अश्नुते भुङ्क्ते सर्वान् निरवशेषान् कामान् काम्यभोगानित्यर्थः । किमस्मदादिवत्पुत्रस्वर्गादीन्पर्यायेण ? नेत्याह - सह युगपत् एकक्षणोपारूढानेव एकयोपलब्ध्या सवितृप्रकाशवन्नित्यया ब्रह्मस्वरूपाव्यतिरिक्तया, यामवोचाम ‘सत्यं ज्ञानम्’ इति । एतत्तदुच्यते - ब्रह्मणा सहेति । ब्रह्मभूतो विद्वान् ब्रह्मस्वरूपेणैव सर्वान्कामान् सह अश्नुते ।
For the word 'krameNa' (sequentially) in the Sutasamhita verse, we have the term 'paryAyeNa'. The meaning is the same: sequentially. The idea is: the shruti says: the knower of Brahman attains the supreme, he experiences, enjoys, all desires (desired objects), in one go, not as an individual, but as Brahman. Here Shankara clarifies that the attainment/realization of Brahman simply means that 'everything is attained' and nothing remains to be attained. In the case of an ajnani, his bhoga is dependent on punya, the presence of the bhogya vastu and the sattva vritti. But in the case of the Jnani such is not the case: just as someone owning a huge reservoir sees that all his water requirements are met here itself without the need for seeking water elsewhere.
The above idea is present in the Suta samhita verse cited.
Needless to say that the Suta samhita text is banned by Madhwas. I heard that the Srivaishnavas have indeed cited from there. I am yet to get a textual reference for this.
warm regards
subbu