I'd like to add to this, if possible. I'm not entirely certain who handles what in the DAS - IB combo.
I understand that DAS provides the data and the software, but after sending the order who handles the routing, and the pre-trade risk management?
DAS touts being colocated at the Nasdaq data center.
Do the orders routed to Nasdaq bypass IB's servers and go straight to DAS and then to Nasdaq? How about the other routes not supported by DAS, but supported by IB?
Do any venue fees change?
I'm sorry if sounding like a noob, but I'm trying to paint a mental map of the road an order takes in a broker + third-party OMS situation.