ok that may be it was too obvious for many of you...
For those interested, the answer is to edit music.ini
found on DATA\AUDIO folder

by adding

[Sound
nickname = music_whatever
type = music
file = audio\music\music_whatever.wav
attenuation = 0

you can add your new soundclip to the game which can be call
from within the room you want by adding to the appropriate room.ini file


[Room_Sound
music = music_whatever

e.q. to add the above mentionned clip to the bar of the first base of my new Hi03 system I edited the
DATA\UNIVERSE\SYSTEMS\HI03\BASES\ROOMS\hi03_01_bar.ini
which in turn was been called by
DATA\UNIVERSE\SYSTEMS\HI03\BASES\hi03_01_base.ini as suggested by the appropriate tutorials found in this board.