Our load balancing cannot split the packets according to their size, the only way to do it is through ports or IP addresses that your router communicates through with the app.
As it's almost impossible to determine which IP's are used to communicate with the app like youtube or gaming as there are many servers - it could be done by using different LAN ports for each thing you do, but that wouldn't be efficient as it would be hard to do only on one network card.
Also, QOS splitting right now exists only on RUT2 and RUT9 devices and there's limited functionality on RUTX series devices.
Regarding the question about triple load balancing - what do you mean by that? Do you mean load balancing through 3 different interfaces like Wired WAN and 2 mobile modems? Then this is possible on RUTX12.