I don’t quite know the answer to your question but wanted to highlight a few things that Varunji has shared over the course of this webinar that may provide some pointers. Sorry, it’s a rather long post!
1. Please see below a portion from his excellent write up called “Why Sanskrit?” It alludes to the origin of Sanskrit/dhatus - more of a how than a why of the Sanskrit roots.
“According to Sanskrit lore, in their seat of deep meditation, the Ṛṣis, or the people responsible for developing Sanskrit, came to experience the universe as a giant set of vibrations. These vibrations were, for them, experienced in the form of sound. They documented the sounds they heard, constantly pulsating in and through each object of their experience, and derived from them the roots of what we now know as Sanskrit. The language that evolved from these roots was just, according to them, a recreation of the sounds they heard in their meditation: the perpetual throb of the vibrating universe itself.”
2. He also mentioned in one of the lectures that ॐ is the substratum of all vibrations. ॐ sounds like A…U…M… (अ ...उ.....म.....) - sort of encapsulates the entire spectrum of sounds/vibrations/Aksharas one can produce between throat (कण्ठः) and lips (ओष्ठः) See his comments below for further pointers:
“Keep meditating on them, and these things will reveal themselves to you. You can then speak from your own experience. All the ऋषिs came to these same conclusions independently, just by meditating on the deeper aspects of life. I hope these realizations come to all of us in due time, too!”
3. He’s been giving pointers in the lectures that Sanskrit is an ‘experiential’ language and we too are capable of experiencing it in due time as we meditate on where the language is taking us! As he says ‘...learning Sanskrit is not just about learning Sanskrit.’
I have had a small taste of the power of this language when I stumbled upon the Bhagavad Gita in Sanskrit a few years ago during an unusually tough phase in my life. I then experienced that the teachings started to unravel at a very personal level even though my Sanskrit knowledge was limited at best! Before this, I had tried but never succeeded in going past the Foreword of the English translations of the Gita! So, not sure if it was the timing or the language or a combination of the two that the Gita suddenly became very up close & personal and continues to be so!
4. And last but not the least, I’d highly encourage you and others to check out Samskrita Bharati -- www.samskritabharati.in or http://www.samskritabharatiusa.org/
This organization conducts a 10-day free course on spoken Sanskrit in many places around the world. I just attended one in Bengaluru and would vouch for the efficacy of its methodology and the enthusiasm that its teachers, organizers, and even students bring towards Sanskrit. For me it was a double treat as I could combine Varunji’s focus on grammar and this course’s focus on the spoken aspect of Sanskrit. Of course, I still have miles to go but have taken the first few baby steps for sure.
May our Sanskrit journey continue to take us to places yet unknown…