Around ??200,000 worth of watches were stolen in the raid on Guest and Philips Jewellers on 6 August.
Humberside Police said four men and two women were arrested on Friday with the assistance of both South Yorkshire and Nottinghamshire Police.
The force said the suspects had been released on police bail.
Six people have been arrested by police investigating an armed robbery at a jewellery shop in Beverley, East Yorkshire.