The thing here is that when Ableton is in use (and some other audio applications), the ASIO (Audio System Input Output) technology is being used. This essentially “bypasses” the Windows Audio panel. It is a lower latency, more directly connected and controlled audio protocol. The browser and Media Player, etc., in Windows do not use ASIO technology. Of course, the headphone knob on the UR will affect everything because it takes effect after the signal has left the computer and just before it is sent to the actual headphones. Personally, I keep the Media Player and Windows volumes pretty high and the output level on the UR unit fairly low. That seems to work pretty well.
HTH