Thanks for sharing your photo, aloncoen.
Your flooring is almost identical in appearance to mine. The brass looks very nice, and my electrician showed me a similar box that he suggested could be modified for speaker cable connectors, but I am convinced there must be a smaller, less obtrusive solution out there. I guess we will just have to keep searching.
My current thinking is that perhaps a finishing carpenter might be able to cut a small removable plug out of the hardwood flooring. This would leave a small hole that speaker cable could be fed through, and hidden by placing the speaker stand above it. When not needed, the speaker stands would be removed, the speaker wire disconnected (or, in my case, pulled back down into the basement below) and the plug inserted to fill the hole. If the carpenter was skillful, the plug should be almost invisible.