The most common and most likely answer to this crossword clue is the 6 letter word DUPLET
D
U
P
L
E
T
Buddy explains!

The straight part
We know that "a pair of sixes maybe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a pair of sixes maybe = duplet.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DUPLET mean?
DUPLET noun- A group of two things.
- An empty box placed above the existing boxes of the beehive in order to allow the colony to expand or store additional honey.
- A tuplet of two notes played in the time of three.