>> They are the same system device but they are separate devices to Mixxx.
>Is there an Indicator, to detect your case? Or do we need a preference option?

A preference option for drift control would be nice. It would also give us a place to explain to the user that the latency is potentially double what we tell them it is when using multiple sound cards with drift control. 

I think a lot of users may get away without the 1 buffer of additional latency though. It would be nice if we could adjust the set-point dynamically. Start with 1 chunk as the target and if drift occurs increase it to 2 chunks. This detection will likely enable within the first 30 seconds of applying a sound configuration so it should not affect the output for long.