[bornacatholic]

I can't find Jungmann's Volume I of the Mass of tne Roman Rite (I lose and find books in my house all the time) but I do vaguely recall he cited a Jewish prayer which response to "The Lord be with you" was "and also with you."

Something close to that (This is off the top of my head). Do you recall anything similar or ever hear/read of that explanation? I'm not claiming Jungmann is definitive or authoritative on this point.

I'm pinging a few others

[Campion]

I don't know, but the Latin text is clearly "Et cum spiritu tuo", which translates word for word as "And with [the] spirit yours", not anywhere close to "And also with you", which would be something like "Et etiam tecum" in Latin.