Hi,
1) How much gain is needed by the Shure SM57 for
comfortable recording
with a low noise floor?
2) Whether the M-Audio Fast Track Pro, Tascam US-144, Alesis IO|2 or
Edirol UA-4FX are able to provide pre-amping with that much gain?
I'm not sure I understand correctly the question...
As for 'noise floor' much for example depends on the input signal,
environment etc. or are you talking about the intrinsic 'noisiness' of
pre-amps on the cited devices?. Maybe if you explain the situation/setup
one could have a clearer picture.
Anyway, because the SM57 is a dynamic microphone you should be ok with
virtually any decent mic preamp: at an extreme limit you could probably
even plug it into your computer's "mic in" (but then of course might as
well use a 10$ skype microphone or something :) ).
Lorenzo.