Hello everyone, this is a strange one for my beginner knowledge.

My father used to have a Yamaha YST-MS25 2.1 speaker system in his computer around 1999 which I loved, and wanted to get one for some time. I bought one on the cheap, made a quick test with my MP4, and it worked fine. Then I connected it to two of my older computers and the sound was totally absent at normal levels, I had to crank the Windows/SBlaster volume up to 100% and the speakers volume knob up to the max as well to hear something.

Shortly after I found another YST-MS25 2.1 set for even cheaper, so I got it to have one in each older computer, but the same problem remains: sounds normal connecting directly to MP4, sound way too low at normal values connecting to my older computers. Both sets came with one cable missing, the one that connects the woofer to the computer in this case, but surely that can't be the problem as it's a simple 3.5mm jack cable, right?

What truly confuses me is that these kinds of speaker systems were primarily designed by Yamaha for computer use, so I'm at a loss here. Why does this huge difference occur between my MP4 test and my computers?

Both computers have a Sound Blaster Live! CT4830, on Win98SE and WinME respectively. As for the speaker set, some technical info here if needed: http://www.megatrade.ru/English/ms25.html

If anyone could help me I will be truly grateful as always, I would really love to have them usable for normal desktop computer use. Happy holidays!

Edit: could it be some capacitors going bad causing resistance? But then again shouldn't it happen with the MP4 as well? Thanks!