After having upgraded with a new power cable on my CDP and sub, I tried measuring the exact distance from the CDP (in the center of my soundstage) to the left and right speaker respectively. They didn't stand in the exact same distance, and I had wondered why my soundstage was a little skewed. Only an inch too much distance with the left speaker did all the difference! When I moved the speaker so they were both in the exact same distance (to a fraction of an centimeter) the soundstage came just right. Much easier to pinpoint every instrument, and much easier to hear the echo from the surrounding walls in the recording room! I'll be damned! Why didn't I think of that sooner?
This way the speakers don't have the same distance to the side walls, and I thought that was essential! But it isn't! Another story with the rear wall though. Distance must be the exact same. There's something to learn every day...