8-track editing

I have edited 8 track (4 x 2 stereo) in reaper for an onsite exhibition. I tested it once with 8 speakers, but cannot access this studio anymore. Now I need to adjust/balance the volume of some tracks, but this is not possible as I can only listen to a stereo track on my desktop. I'd need some help this week and can travel anywhere in London. The whole sound installation is 30 min.