You have selected the default Windows audio device, which is called "Default Audio Device [Direct Sound]" because the default device in Windows, your USB SoundBlaster, is set to Direct Sound.
It is not Best Practice to select the Windows default audio device in MC. In fact, I think it is bad practice, because whenever you change the Windows default audio device, you are also changing the audio device that MC plays to, which could mean that the settings you are using aren't a good match to the device MC is playing to.
If you wish to play to your USB SoundBlaster using Direct Sound, select that option as the Audio Device in MC. It will probably be called "USB SoundBlaster [Direct Sound]" or similar.
I don't know why you experience latency when using MC, but the language you used to describe your setup, and the fact that you have selected the "Default Audio Device [Direct Sound]" in MC rather than "USB SoundBlaster [Direct Sound]" shows that you do not have a full understanding of how audio works in MC, and possibly how audio works in Windows. This is not a criticism. It is an observation.
Also, I don't work for JRiver, so I'm not trying to move "blame" away from it. What I, and others here, are trying to understand is how you have MC set up and hence why you observe latency. It could be a MC software issue, or it could be a misconfiguration. Awesome Donkey and Matt can't reproduce the problem, so whatever it is, it is probably something to do with your environment or setup. It could be the USB on your motherboard. Typically a motherboard will provide some USB ports directly from the chipset, and some from a third party chip. Often those two sources of USB ports have different performance characteristics. So it could be that the ports you have the USB DAC and USB SoundBlaster plugged into do have some latency, or that the driver does when using those ports, particularly if they use a different driver to the Microsoft supplied one. It could be something else.
Post a screenshot like the image I have attached, showing all the available audio devices, both in the first group and the "More" group.
Also, when you were playing to your USB DAC you said you were using WASAPI. Please confirm which audio device from the list above you had selected. Also, as Foobar2000 seeks instantly, which audio device is it playing to?