I’m surprised you seem so confused. There is no formal study of which I’m aware, but Ansel Adams has a table and graph in one of his books (I think it was “The Camera” or “The Negative”, but it may have been the one he did on prints – I’ve forgotten what that one was called).
Essentially, Soul cannot be captured by digital means (as we’ve all guessed – one can’t reduce God’s Own transport to 1’s and 0’s … you would need to at least have a few 3’s and 4’s in there somewhere). HOWEVER, a good artist can transcend his medium to some extent, so the best artists using digital CAN capture some soul, but this is capped at 10%.
Soul transmission is enhanced by a) lack of colour and b) film format (also “contrast” but that’s a lengthy topic). As you are using 8×10’s you can still capture a lot of soul – even in colour – probably about 60% or so. Converting to B/W would destroy all of this (as can be clearly seen in your examples) as this is achieved through digital means and we are back to the 10% soul conveyance maximum again.
Looking up the tables in Ansel Adam’s book you can see that if you had have been shooting B/W in your Fuji 6×9, that would have had a 70% maximum soul conveyance, however your predilection for using flash would have reduced that by 15%, to a 55% maximum. Shooting in 8×10 with real B/W film (deduct 5% for any film other than Tri-X), gets you up to the maximum allowable 85% soul conveyance (if you don’t use a red filter – souls can’t get through this lightwave frequency … this renders the theoretical maximum “high contrast” soul conveyance a bit more difficult to achieve in practice).
Theoretically, you can get a 100% soul transmittance if you shot a 20×24, B/W photo of Aretha Franklin and Contact Printed, but no one has ever attempted this madness to see if they can, indeed, touch the face of God.
PS. Leica doesn’t need to advertise the “soul” of their Monochrom (are you SURE that they don’t actually do so ? They get pretty close to it.) as all their adherents will do so for them, and the profit margins on their cameras and lenses is so slim that they can’t afford any marketing.