What Vince said is true for making general progress.
Upekkha100’s question is specifically on attaining the Sotapanna stage. In the Sotāpattiphala Sutta (SN 55.55) it says: “Cattārome, bhikkhave, dhammā bhāvitā bahulīkatā sotāpattiphalasacchikiriyāya saṃvattanti. Katame cattāro? Sappurisasaṃsevo, saddhammassavanaṃ, yonisomanasikāro, dhammānudhammappaṭipatti..”
So, “saddhamma savanaṃ” or “listening to correct Dhamma” is one of the 4 requirements to attain the Sotapanna stage.
Now, as upekkha says: “I would think that the energy that was emanating from the Ariya’s mind(as the desana was being delivered) would be able to reach the mind of X.” is likely to play a role.
The question is whether that “live listening” is necessary or whether a recorded desana is sufficient.
We may never get a conclusive answer, but Waharaka Thero probably had some valid reasons to say that it would be sufficient to listen to a recorded desana by an Ariya.
Here is another thing to think about:
As I explained in an answer to another question today, we need to think about how the “sota indriya” (which is not the same as the physical ear) works.
Sound waves are transmitted through air as waves of air compressions, just like water wave that propagate outwards when a stone is dropped in water.
– Air compressions hit the ear drum inside “the physical ear”, and makes it vibrate.
– Those vibrations are sent to the brain and the brain converts them to a “sound signal” (this is how a microphone converts spoken words to an electric signal too) which it then transmits to the “sota pasada rupa” located close to the hadaya vatthu in the mental body (gandhabba); see, “Brain – Interface between Mind and Body“.
Now, when a recorded signal is played back, it re-creates that same sound wave propagating through air. Therefore, whether listening alive or via listening to a recording, one’s ear drums will generate the same signal.
Therefore, other than effect of being exposed to the “javana energy of cittas” while listening to a live desana (mentioned above), the actual sound reaching the sota pasada rupa will be the same.
So, while it could be better to listen directly, listening to a recorded desana is likely to be enough.
From the accounts of some people at this forum, and also according to those who have listened to Abhaya Thero’s desanas on internet, listening to a recorded desana seems to be sufficient.