How to implement such a replace-regexp in interactive mode?

["Home_king" <home_king@163.com>]

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In Dired mode, to modify marked files according to a specified regular expression, as known, push "Q" after you marked them. 
However, I find I can't use "\\1" to quote strings between "\\(" and "\\)" (By the way, strangely, it seems that I must use "\(" and "\)" instead in such "Q" interactive query mode). 
For example, some files has below style:
---------------------------------------
...
aaa
bbb
ccc
... 
---------------------------------------
And I want to add a line "XXX" between "aaa" and "bbb". 
I push "Q" and I use "^\(a+\)$" for regexp parameter and "\1\nXXX" for substitue parameter, but it fails ...

On the other hand, I succedd using my perl script:
-----------------------------------------
#!/usr/bin/perl
($#ARGV <= 0) || print "Your must input filename to process!\n";
open OBJFILE, "$ARGV[0]" or die "$!";
open TMPFILE, ">_tmpfile"; 
while (<OBJFILE>) {
    s/^(bbb$)/$1\nXXX/g;
    select TMPFILE;
    print;
}
`mv -f _tmpfile $ARGV[0] && rm -f _tmpfile`;
-----------------------------------------

Help!

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