The subclass number 856 visa is an onshore employer sponsored visa granted under the Employer Nomination Scheme.
In short, you are at liberty to work for whoever you choose in Australia - it need not be the employer that sponsored you for the 856 visa.
See also:
Employer Nomination Scheme (Subclass 121/856)
Best regards.
__________________
Managing Director, Go Matilda,
http://www.gomatilda.com
Registered Migration Agent Number 0102534 and Chartered Accountant (England & Wales, and Australia)
Offices in the UK and in Australia