I have a mixer with a USB interface. The mixer has two channel strips that can receive audio from the USB audio channels and inject it into the channel strips, thus allowing you to independently fade, pan, etc. those two channels. To the PC, the device shows up as a four-channel sound card. To play to one strip, you can play normal stereo audio which will go to the "USB 1-2" strip. To use the second strip however, you need to send audio to the third and fourth channels of the USB audio device.
This works great for my DAW (I can select which channels I want going to USB 1-2 and USB 3-4), but I want to be able to use this for generic applications. Since very few applications not built for audio production are aware of anything more than stereo output, I need some way to create virtual sound cards that can make USB 3-4 appear as another "normal" stereo sound card that applications can send audio to. Basically, I want to send some applications to USB 1-2 and others to USB 3-4.
Coming from Mac OS, I used an application called "Loopback" that allowed you to do this. You could create virtual sound cards, map their in/out channels any way you choose, and so on. So I could create a virtual "USB 3-4" sound card and assign its Ch1 output to USB-3 and Ch2 to USB-4. Then any audio I played to that virtual sound card appeared on USB 3-4 with no noticeable latency. (I could also flip stereo if I wanted to for whatever reason - map Ch1 to USB-4 etc). There seems to be no good equivalent on Windows, at least with near-zero latency and with the flexibility of the Mac version. VB-Audio seems to have a couple offerings, but it doesn't seem to have this exact functionality without some really kludgy workarounds or hacks, and in either case it introduces a ton of latency. Virtual Audio Cable has the same issue, plus for that instance you need a "repeater" which adds even more latency (since VAC is basically a virtual internal pipe, while you can send whatever application audio you want to the VAC device, you still need something to "listen" to the virtual sound card and then "play" it through the desired hardware device channels - hence the repeater)
Are there any Windows programs (paid is OK) that will function similar to "Loopback", allowing me to create virtual sound cards and map the in/out channels as I desire, with as close to zero latency as possible? (Obviously true zero latency is impossible, and even Loopback I'm sure is adding some small amount of latency, but it's low enough to be unnoticeable.)