etymological discussions are interesting and everything, but they're ultimately reconstructive guesswork, and you have to approach them with a large dose of skepticism. i'm more interested in looking at the issue from a comparative religions, syncretic studies or origin of religions type perspective, and tracing the influence of the amen cult on the obscured origins of hebrew religion is something that's well grounded. so, you can put up your etymological dissent if you must, but i find the premise of the maintenance of an amen chant through the ages to be the more convincing explanation as to why humans get together and sing this word in community with one another. i see no convincing reason why we would sing statements of affirmations to each other, but i see very good reasons why we would chant the name of the creator deity, as a form of sympathetic magic. it's just a question of looking at these two arguments and deciding which one is more compelling.

so, i mean, i don't have an answer for the critical linguists, other than to suggest there doesn't have to be one. these derivations are possible, but not necessary; there's no reason that reality has to conform to the tidy math. 

further, if you consider how the word would have ended up in the hebrew language if it was loaned from egyptian, a concept of transliteration is more likely than a conversion from hieroglyphs. so, pointing out that they have different starting letters isn't that convincing, if you consider the likelihood of transliteration in the loan process. i mean, these are the kinds of debates you have - the proposed etymology is a possibility, sure, but there's no causal implication around it, and if other evidence suggests otherwise then it's possibly just wrong, despite making absolute sense, as a deduction from the theory.