@Straticah I think you more or less have hit upon the best solution, and this sort of issue isn't at all unique to HISE. Understanding the gain added/reduced by any one particular effect, sampler, or synth in isolation and compensating it with a nonlinear gain node is probably the solution, outside of compression which as @ustk hinted at, can squash the sound or introduce unwanted artefacts.
Personally when working on FX I'll introduce a gain node in my scriptFx chain which does precisely this. I do agree that it would be nice to have a meter node which could help us analyse the gain output at any point in the chain, but at the end of the day you have to trust your ears!