How do people control amplitude: PianoTeq, soundcard, amp, mixer?

I know what the conventional wisdom is for traditional electric instruments like an electric guitar: turn up the amp as high as you can without feedback and then use the volume control on the instrument to bring the level down to what you want.

But with vsti's, we have 3-5 things affecting amplifcation:

1. The volume knob on the sound card or the software control on the driver interface for the sound card.

2. In Windows, the volume control in the Windows mixer. (Which somehow still has an effect, even though I'm not using the internal sound drivers.)

3. The vsti's (Pianoteq's) volume control. Convention says to keep this at around -6 to give room for overhead, but I often find myself raising it higher.

4. If we are not using headphones, the volume knob on an amp or on powered monitors.

5. If running through a mixing board, that board's volume controls.

Is there firm knowledge of how these things should be set so that the signal arrives at the headphones\ monitors without either being weakened or distorted. Everything at maximum except the PianoTeq volume control? (That would seem to follow the electric guitar logic.)

I've just fallen into the habit of keeping my external soundcard at about half+ volume and keeping Pianoteq at anywhere from -6 to 0, depending on the preset.