One of the devices will stream slightly faster than the other, so some mechanism is needed to keep the two streams 100% in sync with each other.
The windows mixer has the capacity to do this. VB Audio probably runs through the mixer.
Come to think of it, JRiver as a virtual sound card might work too. You can activate the wdm audio driver in JRiver. Then it will appear as a selectable speaker in Windows. You set it as default speakers and make it listen to the input of your ADC. And then, in jriver, you send the audio to the convolver.
Maybe Asio4All has some way of keeping the two streams in sync as well, but it runs underneath the windows mixer so it needs its own solution.
There's no way to tell for sure whether any of these will work without trying.