Mr.- I have the craptastic logitech "X5bla" system on my desktop and I can't even listen to MP3 files on them unless I have the volume turned down slightly and causes the amp to distort. So your softsynth is probably too loud. But anyhow, all distortions have their own characters. What you're hearing is a harsh and defined digital clipping sound of information being out of range, since CDs play ok your amp is probably fine. When an amp distorts it will usually sound smoother, less clicky than digital clipping. When your speaker is cooked it will usually sound bad around specific energies of sound(?) like, bass will sound terrible and mids sound slightly airy / fuzzy at low volume and then as it gets lowder it all starts to sound like a flag in the wind.
