V9 UPDATE:  the variable "Value" has been renamed "Input". So, same instructions but the external triggers 
(e.g. Timeline and slider) now target "Input" :)

Instructions for using ValueMapRelay Logic Brick to control absolute audiosource volume from a slider, but
fade-out using e.g. Timeline, and subsequently fade-in volume, yet only reaching absolute volume level set by UI slider.


1) Add ValueMapRelay plugin to Audiosource - or any atom of choice, for ease here, let's just put it on the Audiosource :)
2) next, select ValueMapRelay "Value Actions" = (atom)Audiosource/(receiver)Audiosource/(target)Volume Start 0.000 -> End 1.000

3) ValueMapReplay variables settings:

a) "Value" controlled by external trigger - e.g. Timeline fading volume.
b) "Input From" set to 0.000
c) "Input To" set to 1.000
d) "Output From" set to 0.000
e) "Output To" controlled by external trigger - e.g. slider for volume.

Next:

3) Add slider trigger, name "Volume"
4) Slider trigger action = (atom)Audiosource/(receiver)ValueMapRelay/(target)"Output To" Start 0.000 -> End 1.000

External trigger e.g. Timeline for volume fade:

5) Trigger action - instant or timed = (atom)Audiosource/(receiver)ValueMapRelay/(target)"Value" 0.000 to fade out,
or 1.000 to fade-in/instantly make noise again

6) Make another coffee and muse that this would've been easier to work out if I hadn't been woken at 04:30 by neighbours 
screaming obscenities at each other.