Daeman translated this as 'Go get them'. Can colleagues explain the exact origin & meaning of what seems to be a slang expression?
First of all, the full phrase is "Γεια σου,
insert name here, με τα κλαρίνα σου!"
Secondly, Daeman did not translate it; he just found it translated this way
in that video, and although he doesn't object much to that translation, he would rather render it as "Way to go!" perhaps, since it's a colloquial way to praise someone. Actually, the "Γεια σου" part carries that meaning, and after the name comes the last part "με τον / την / το / τους / τις / τα
whatever we admire and praise the person for" making it more specific.
See also
γεια:
β. γεια στα χέρια σου, εγκωμιαστικά σε κπ. που έφτιαξε κτ. πετυχημένο. γεια στο στόμα σου, εγκωμιαστικά σε κπ. που είπε κτ. πετυχημένο.
Thirdly, I believe the origin of the particular one with "κλαρίνο" is an exclamation praising the musicians at a country (folk) fair or wedding or any kind of feast in general, where κλαρίνα (clarinets) are traditionally used in most parts of the Greek mainland as the main instrument carrying the melody and solos, and urging them to go on like that
(I've often heard it used that way in such instances).
From there, it was not a big leap at all for the phrase to be adopted for use towards any musician, like bouzouki or baglama players as addressed to Markos Vamvakaris here: «Γεια σου, Μάρκο, με τον μπαγλαμά σου!»
Anyway, it's generally said in any instance where you admiringly praise someone for something they expertly do, e.g. in football, "Γεια σου,
insert football player name here, με τις ντρίμπλες σου!", most of the time earnestly, but of course such phrases are also often used playfully as a joke or with a note of irony.
Come to think of it,
in that video it's certainly used mockingly, not to mention that the plural, particularly when addressed to a woman and in such a comedy, probably has other connotations, of a sexual nature.
The answer, my friend, may well be blowing with the reeds.