Problems with boss — hard ones to describe (9)

'problems' is the definition.
(I've seen this in another clue)

'boss hard ones to describe' is the wordplay.
'boss' becomes 'head' (synonyms).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'ones' becomes 'aces' ('ace' can be a synonym of 'one').
'to describe' means one lot of letters goes inside another.
'h' inserted within 'aces' is 'aches'.
'head'+'aches'='HEADACHES'

'with' is the link.