You can use ASIO4ALL to set up onboard 5.1 solutions (if it exists) with 2 independent stereo outs.
DJ2GO uses Asio4all in order to facilitate that too.
Traktor Audio 2 (£5 more) has the same functionality but dedicated drivers and far, far better latency results because of it along with a better set of audio converters.
To answer the question however you can’t combine drivers/interfaces so no, you can’t use the Dynamode along with the on board. I’m afraid the only way it’s going to work is to install ASIO4ALL and tweak away at the 5.1 outputs (if the board has them) or purchase an interface designed to do it.