This night I transferred my first batch of music in .wav format from iTunes to BM5. Result: 

1. Only my only .mp3 piece of musik is shown correct

2. All the other music is named as "unknown" artist, no cover artwork is shown, no piece of music is in any right order (even not in the menue point Album) they are sorted as piece 1 of CD 1, piece 1 of CD 2, piece 1 of CD 3....

what have i done wrong ?

Seems to be a problem of the .wav format. I checked it with .mp3 and everything is fine. But I dont like to use .mp3 so what would be the next best format after .wav I can use at the BeoMaster5 ?

On a side note it can be noted that Beomedia 1 does the same thing. Most annoying, so any tips are most welcome!

That is because WAV-files can not hold tag's like covers and titel/artist information. Use WMA (losless) and you will see that everything will be alright!

Yes, I can confirm:

Just use WMA losless - this is WAV/CD-quality with all the benefit (cover art, track informations etc.)