Didn't watch the vid yet but have done my own M8 vs 10 comparisons. The external speakers on the M8 present a fuller, warmer sonic signature. Though the 10 sounds more "tinny" in direct comparison to the M8, it actually has a strong point in that the midrange is full, forward, and articulate, making voices really sound great. Also, even though they essentially have around the same volume, the 10 is much easier to hear from a distance because our ears are more sensitive to the midrange (vocal range) which the 10 excels at.
Interestingly, there seems to be a little more actual bass coming form the 10's speaker port, but it doesn't travel far at all and sounds bass-light compared to the M8, unless you are holding it in a certain way.
Little tip; try setting your 10 on different surfaces and aiming it in different directions as this can influence the sound quality greatly.
Headphone audio is another matter entirely. The 10 trumps all.