Could be a phase issue (black and red interconnects switched). Some interconnects are directional too. This would be the easiest thing to look for. But I doubt that there's a phase problem.
I'd certainly expect the room to make a difference with bass reproduction and collapsed soundstage. How are speakers/listener positioned in each room? Obviously in a 12 ft x 11 ft room you don't have many options, but see if using an angled, non-symetrical setup helps. You probably need room treatments, but of course that would make the small room even smaller.
Some of the improvements you're hearing is probably due to the extra heft provided by going mono.
Don't know why, but most pieces improve after a "re-break-in" period.
