I don't understand german either, but here's my guess as to what you were trying to do.
ioFTPD versions > 7.4 use OpenSSL and the 'Min_Cipher_Strength' / 'Max_Cipher_Strength' options have been replaced by the 'OpenSSL_Ciphers' option, see
http://www.openssl.org/docs/apps/ciphers.html for details.
To see the full list of ciphers supported use 'site ciphers' command from a 'M' flagged (master) account. You can force 168 bit versions of the cipher suite to be preferred by listing them first... maybe something like this would work.
OpenSSL_Ciphers = DES-CBC3-SHA:DEFAULT:!LOW:!EXPORT
I STRONGLY suggest making sure the 'Encryption_Protocol' option is COMMENTED out. Trust me, limiting this is usually a bad thing.