"So in general, is it not possible to do a multi-array assignment in a single line, i.e.: (@a, @b) = <some_expression>"

That's correct with the syntax you're using there; however, you can do it with references. Here's a rather contrived example to demonstrate.

#!/usr/bin/env perl -l

use strict;
use warnings;

my ($letters, $digits) = get_arrays();

print "Letters REF: $letters";
print "Letters: @$letters";
print for @$letters;
print "Digits REF: $digits";
print "Digits: @$digits";
print for @$digits;

sub get_arrays {
    my @three_letters = qw{A B C};
    my @three_digits = qw{1 2 3};
    return (\@three_letters, \@three_digits);
}
[download]

Output:

Letters REF: ARRAY(0x7ff684047ad0)
Letters: A B C
A
B
C
Digits REF: ARRAY(0x7ff684047938)
Digits: 1 2 3
1
2
3
[download]

If you're unfamiliar with references, a good place to start is "perlreftut - Mark's very short tutorial about references". In the "The Rest" section, you'll find links to more detailed documentation on this topic.