Thanks for the pic, maybe some with garage door installation knowledge can add some information about your pic?
With the little knowledge I have (my door is 8' x 18') and the install looks very similar, but I have only 2 door springs (each very long and thick in rod diameter) and they do not bow like the 4 door springs you have?
I am just guessing here, but I still believe the garage door can/should be balanced with the properly sized door springs in order to manually open the door with ease.
I also think maybe your door springs might be undersized since they really appear to have a good size bow in them?
Most everyone here is concerned with the electrical hazards (and rightly so) but I am also concerned with the "falling garage door hazard" if something fails like a broken cable that winds up on the drum, because it sounds like it would drop like a ton of bricks.
I do think Fuddy has a very simple and safe solution, post #61, to your problem a long with a previous post.
I do hope you find your solution to your problem.
I know this isn't in regard to your solution, but I purchased a Roybi garage door opener a couple of years ago with wi fi, and a 18 volt battery back up/charger, belt driven.
I cannot believe how quiet it runs and just love the soft start/stop feature.
I also purchased and plugged in to this opener (think it has 7 stations) a blue tooth speaker, a multi speed fan, and a 110v hose reel, sorry this has nothing to do with your issue.
Good luck,
KC