US broker Knight Capital Group is set to buy Astor Asset Management for $20 million in cash and stock as it moves to expand its services into the investment advisory sector.

New Jersey head-quartered KCG will diversify its revenue stream with its purchase of AAM, a money managing firm that focuses on growth through macro-economic strategy and exchange-traded fund portfolio construction.

"Astor Asset Management has undergone rapid growth by providing active management and diversification across sectors and asset classes at a relatively low expense ratio using ETFs," said Thomas Joyce, chairman and chief executive officer of KCG.

Astor Asset Management, founded in 2001 by Robert Stein, is based in Chicago, Illinois and has $560 million in assets under management in the Astor Long/Short ETF Mutual Fund, and in ETFs in separate accounts.