Kudos for use of "whilst!"
to your question, 0dB will be louder than -10, etc...
The key component in this is the signal going to the Sub. Auto-On or Music-Sense features rely on a certain amount of voltage entering the Sub through it's input(s). How sensitive any given Sub is to this signal is not standardized.
One trick, if your Sub has two inputs like an LFE and a second RCA in is that you can split you signal Sub Out cable with a Y and plug both into the Sub... This may increase the signal your Sub sees enough to keep the Sub on.
Also, turning up the volume will give the Sub enough to keep it on. *blushes