Oh yes, the TENC and TXXX stuff is still used/set internally - I'll remove that from the next version!
However, if you want to update your 'own' metadata to the Shoutcast v2 server you would need to use your own call to:
instead of using the "SHOUTcast.UpdateTitle" method!
string metadata = "...well formed shoutcast xml data...";
BassEnc.BASS_Encode_CastSendMeta(Encoder.EncoderHandle, BASSEncodeMetaDataType.BASS_METADATA_XML_SHOUTCAST, metadata);
This way you have full control over any metadata you are sending/updating.
The internal "SHOUTcast.UpdateTitle" method is doing nothing else.
Just take a look to the SHOUTcast documentation and create a well formed SHOUTcast meta data string using UTF-8 encoding.
Same goes with the the Artwork.
Use one of the "BASSEncodeMetaDataType.BASS_METADATA_BIN_ALBUMART_xxx" flags instead.
Note, that the SHOUtcast server can not display the artwork itself.
It always anyhow just tell you, that it is there - and when it tells you this, all is fine.
It is just, that future players resp. the new SHOUtcast directory service might one one day use the artwork pictures transmitted.