As SuicideJuknie points out, your substitution is failing because your regex doesn't match. I thought it was because your .+ in the middle of your pattern is 'greedy' so is matching right to the end of the string, and your Track part can't match. However this is not right because perlre tells us that

" . Match any character (except newline) "

So really it is failing because you don't have 'Track' on the same line as the 'CD_TEXT' bit.

Some playing around and I got to this, which does the job, and should get you to the answer:

use warnings;
use strict;

my $string = <<END;
CD_DA

CD_TEXT {
  LANGUAGE_MAP {
    0: 9
  }
  LANGUAGE 0 {
    TITLE "Multi-01"
    PERFORMER ""
    SIZE_INFO { 1,  1, 19,  0,  3,  2,  0,  0,  0,  0,  0,  0,
                0,  0,  0,  0,  0,  0,  0,  3,  7,  0,  0,  0,
                0,  0,  0,  0,  9,  0,  0,  0,  0,  0,  0,  0}
  }
}

// Track 1
END

## include *all* characters between markers
if ( $string =~ m|(CD_TEXT[\W\w]+)Track|){

    print "\'$1\' Matched!\n";
}
else {
    print "\'$string\' did not match...\n";
}
__END__
'CD_TEXT {
  LANGUAGE_MAP {
    0: 9
  }
  LANGUAGE 0 {
    TITLE "Multi-01"
    PERFORMER ""
    SIZE_INFO { 1,  1, 19,  0,  3,  2,  0,  0,  0,  0,  0,  0,
                0,  0,  0,  0,  0,  0,  0,  3,  7,  0,  0,  0,
                0,  0,  0,  0,  9,  0,  0,  0,  0,  0,  0,  0}
  }
}

// ' Matched!
[download]

Hope this 'elfs.