actually, thanks to QuickBMS and its wonderful author, I have managed to finally get a look of all the files.
this is the script
###
get FILES short
get DUMMY byte
get DUMMY byte
for i = 0 < FILES
get NAME_CRC long
next i
for i = 0 < FILES
get SIZE long
get OFFSET long
get DUMMY long
log "" OFFSET SIZE
next i
###
But, but, it extract a series of MUS (audio/BGM) files and a load of .dat files which I have no idea how to actually read. the result is the same form either the DAT file of the PC (GOG re-release) or the Ps2 file, extracted from the ISO.
Soul Spiral, on the other hand, yields a series of unrecognized formats: .smf, .drm, .vrm. I'd say one of those 3 could be the streamed audio (probably SMF), but no tool I have will allow me to check it. can someone help?
UPDATE: DRM files, are, in fact, archives. Turfster's tool for tomb raider legends Graverobber managed to read them for the TR game, but not for this one.
UPDATE2: the key could lie in the .MUL files extracted off the DAT archive. but, MUL2wav will crash when converting some of the files, while it will convert all the BGM.