Wow amazing, so I've managed to solve my own problem, but sharing for anyone else facing this issue in the future.
Basically, by chance, I found in an old bag of cables a dual 1/4 inch stereo cable down directly to a single 1/8 auxiliary. I've plugged the two 1/4 into my line outs, and the single 1/8th into my speakers, and stereo is working.
I guess that using an adapter between the 1/4 down to 1/8 wasn't cut out for the job of handling stereo information.
Jollier's post in UX1 Stereo output- using an auxiliary cable and keep stereo sound? was marked as the answer