Man Utd shares dip in choppy Frankfurt trading as Mourinho hire expected

* Stock opens up in Frankfurt but then falls back * Man Utd's main stock market listing is in New York * Man Utd's NY shares down around 6 pct so far in 2016 (Adds detail) LONDON, May 23 (Reuters) - Shares in English soccer giant Manchester United slipped in volatile trading on the Frankfurt Stock Exchange on Monday, following media reports the club was set to replace its manager with former Chelsea boss Jose Mourinho. Manchester United's main stock market listing is in New York , although it ha