Two Speakers in PC, Only One Channel Detected

I use two Yamaha MS5PA speakers, originally purchased for an S90 ES synthesizer, with my computer.


The only way that I could come up with to get both to work at the same time with my laptop was by connecting them using a 3.5 mm in/ 2 x 3.5 mm out spliter, but I also had to use a 3.5 to 6.3mm adapter for each speaker cable, as the plugs are 6.3 mm and cannot be connected to the PC directly.


Aside from the clunky setup (the cables are massive and heavy, and what sticks out of my audio jack looks like something out of a horror movie), I am bothered because only one channel (left) seems to be working.


I picked this up while listening to songs and noticing that certain parts of songs were partly quieter or altogether inaudible,just as when you only listen to certain songs with only one earphone. I confirmed this by moving the 'Main Volume' slider in my Realtek HD Audio Manager completely to the left and hearing no difference, and then to the right and completely muting all sound.


Does anyone know why my system is only picking up one channel, and why it happens to be the left? I've had this issue on 2 computers. Generally, the sound quality is acceptable, even if there are some imperfections (on account of the connection, not the speakers, sound card or drivers).


Would purchasing a stereo to mono cable (2 x 6.3 mm -> 3.5 mm) alleviate or correct this issue?