On both machines when using gnome-volume-control it stays in 150 %. It is only when I play with kmix, it drops to normal sound level.
If you try to adjust with PA Vol Cntrl the same thing happens ... cannot make a small adjustment ... drops from 150 to 100 immeditely 
You have installed pulseaudio? Texstars guide is good for that purpose. Install pavucontrol now and after that open it. Go to out going device and look for left/right volume max. You can only get 100 %, but after doing the trick in gnome-volume-control you should se it will show you 150 % in out going device. If not, I will look if there is any solution for you. Like I pointed out before, 2 different machines and it works like a dream. That does not really help you. 
You misunderstand .....
Do the adjustment with gnome vol cntrl .... raising the top level to 150%
Now try to adjust that vol level with anything else ..... mixer, PA vol ctrl or other.
It invariably fails to allow any adjustment ..... it will drop immediately to 100% and can then be adjusted from 0 to 100 only.
Because of this, your solution is not easily applied to other situations ..... I use PA and Kmix for instance ..... although I have used gnome-media for years as it was the only reliable 'simple' way to record since krec always seemed to be messed up.
Now if your solution could have a volume control in the tray associated with it, that allowed adjustment, then it would be extremely useful for many people.
Have you found any such vol control that will allow this adjustment?
It would be great if you did.
If there is one member on this forum promoting pulseaudio all the way, that one is Just19!

Yeah, I have been a bit of a 'fan-boy' since I first got to grips with it .... and the later 'task' package etc has made it very easy now to install correctly. Thankfully the days of creating and editing config files for it are gone for the most part.

Being a bit of a 'gadget freak' PA is marvellous at allowing the various audio devices to be finely controlled .... I have played with usb speakers, wireless headset+MIC, bluetooth earphone+MIC, on board audio and PCI audio card ..... all working and controllable in the one PC at the same time - different applications using the different devices for source and sink. ..... see I said I was a 'fan-boy'
