If you want to combine your sound cards you can use the pulseaudio combine module.
Add these lines to your etc/pulse/default.pa:
It is explained here:
#Make both card play simultaneously
load-module module-oss-mmap device="/dev/dsp0" sink_name=output0
load-module module-oss-mmap device="/dev/dsp1" sink_name=output1
load-module module-combine sink_name=combined master=output0 slaves=output1
Then you will see it in the PA Volume Control listed as Simultaneous Output.....like in the attachment below:
Then you can select it in Playback by right clicking on the stream and using move stream. I use it for my two sound cards and it works very well. They stay in sync and I can select which streams I want to go to each card or to both.