Elimina punti e spazi e fai un semplice confronto:

codice:
$list[] = 'MARMI';
$list[] = 'M.A.R.M.I';
$list[] = 'MAR.MI';
$list[] = 'MA RMI';
$list[] = 'SRL MA.R.MI INDUSTRIE';
$list[] = 'MARXI';
$list[] = "MAR'MI";

$search = 'MARMI';

foreach ( $list as $string ) {
    $subject = preg_replace('/[. ]/', '', $string);
    if ( stripos($subject, $search) !== FALSE ) {
        echo "$string ok\n";
    } else {
        echo "$string no\n";
    }
}