It would be cool to have a real integrated audio gain amplifier for each track and instruments (no matter they are samples or vsti, it would do the same audio gain change for all type of instruments, as a real mixing console).
Sadly it's technically simply not possible with the current mixer to over-amplify samples. However, you could add a dummy plugin (e.g. ParamEq) for the samples you want to amplify and then adjust that plugin's gain.
Yes, that's what I always do, but it's pretty tedious.