$re = '/(.*?): (.*)/m';
$str = 'Matthäuspassion, SWV 479: Introitus:Test
Matthäuspassion, SWV 479:Introitus:Test
letztlich
Matthäuspassion, SWV 479: Introitus - Test
Erster Text, zweiter Text : Dritter Text
Vierter Text, fünfter Text : Sechster Text
Siebter Text, achter Text : Neunter Text';
$subst = "$1 xxx $2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php