Which celestial races other than Devas can meditate on Brahman?
Upon a closer study, it appears that all celestial races can meditate on Brahman.
According to the commentaries, the Devas and others are qualified to meditate on Brahman merely because they have the desire and capability to do so. They have the desire because they can experience suffering, ...
For Bhagavad Gita, you may want to check out the work of T.G. Mainkar
The book is
A comparative study of the commentaries on the Bhagavad Gita by T.G. Mainkar
I believe it was published by Motilal Banarsidas, though I don't know if it still remains in print. http://www.mlbd.in
What is Ramanujacharya's argument that the Upanishads must be true if they grant Moksha?
He's not talking about moksha in that passage. He's saying that an idea that we think is false, won't actually convey any satisfaction to us:
When it is ascertained that a thing has no real existence, the mere knowledge or idea of the thing does not gratify. The ...
Do the Devata Kanda sutras declare that Narayana is Brahman?
Yes. The last three sutras are:
Ante Harau Taddarshanat - Ultimately Hari is to be meditated upon
Sa Vishnuraha Hi - He is called Vishnu
Tam Brahmetyachakshate, Tam Brahmetyachakshate - He is announced as Brahman, he
is announced as Brahman
These sutras are authentic because they are cited by ...