Download "Audio Manager" (actually, buy the pro version, it's more than worth it). This app allows you to create "profiles" that you can use to instantly change the volume levels for all volume sliders. I created silent, vibrate, normal and loud profiles, and put shortcuts for them on my home screen. Now, I almost never touch the volume toggle. I just hit the profile i want and all volume levels get set instantly. This includes instant changes to ringtones (if you wanted to use a different ringtone for your loud profile vs. your normal profile) ... same with alarms, notifications, etc. This app controls ALL of that stuff at the touch of a button, including turn vibration on/off ...
Hope that works for you since there's no way to use a single 'slider' for all volumes at once.