Well, the mystery deepens...
As the monster.sou file was 256mb large, it was too big for my CF card. Instead i did this...
First I converted the monster.sou file from Sam & Max instead. When testing it on my Ipaq, the same phenomena happened. Only the sounds of non-voice effects was played, plus the music. But one voice was acctually played, but only if you skipped the credits in the begining of the game. It was the "Well, that was a plesantly understated credit sequence" line. Nothing else. It also played direct after I pressed the "skip to next comment" button. (that means it played too soon)
After this, I deleted every file and transfered the unconverted monster.sou file. When playing the game with it, all sounds is where they are supposed to be.
Something must be wrong either in the Sou2mp3 converter, or with the extraction/indexing when used on my Ipaq 2210. (Since I guess that no-one else have duplicated this bizzare problem.)
Has the index file system different type of markers for sound-effects and voice-effects?
Example: SE0001=adress1,SE0002=adress4,SE0003=adress5 and VE0001=adress2, VE0002=adress3, VE0003=adress6 etc.
Can someone with an Ipaq 2210 please try these games and see what happens then? Is it my unit, or is it a Pda specific problem?