The issue isn't related to JRiver. It is due to the fact that two stereo soundcards won't be clocked the same unless they are both connected via SPDIF to the same master clock or if they have word clock output/input. Most people can't do that with two consumer stereo soundcards.
Yes, a variable delay would be related to what appens in sound cards, dacs, drivers etc.
But my question is not related to delay. My question is : can new versions of JRiver use 2 stereo sound cards to build, for example a 2.2 configuration ? (whatever it would create or not any variable delay).
If JRiver latest version still can't do this (use 2 different stereo sound cards), does anyone know any digital soundcard (USB or PCIe) with 2 digital stereo out chanels (which means 2 spdif out, or 2 optical out or 2 aes/ebu out or a mix of these) that JRiver can use to make a 2.2 configuration (using convolution filtering).
Lynx AES16 and some RME cards apparently can do it but I find them two expensive for what I want to do (at least at this stage of setup and test results).
Can you explain more why you want digital outputs? SPDIF only carries two channels of PCM.
I want digital outputs because I want to use external high quality DACs.