Ah ha! I have got it. This portion of the encrypted signal is using the Playfair cipher (unrelated to the subject of the bust it seems) and uses the artist's first name as the key.

The encrypted keyword is:
"TP FH AQ".

 

Use the chart to break the code. 

1) "TP". Since these are in the same row, what letters are to the left of each?


2) "FH". Since these are not in the same row or column, form a rectangle with "F" and "H" as the corners. What two letters make up the other two corners?

 

3) "AQ". Since these are not in the same row or column, form a rectangle with "A" and "Q" as the corners. What two letters make up the other two corners?

What six letters did you get? They will form final keyword for this Bonus Challenge clue.