Music for speaker setup?

I am getting serious about positioning my speakers. I have a small, irregularly shaped room and small changes in placement can result in significant changes to sound.

It would be very helpful if I had a few recordings that were "known quantities" as far as imaging. What happens is that I get the speakers positioned where they seem to work well with some recordings, then I put on another disk and hear something I don't expect (off-center soloist, for instance). But you never know; maybe in this particular recording the soloist is supposed to be off-center. In classical and many jazz recordings, the engineers aim to reproduce the sound of the actual performance, so a photo or description of how the performers were arranged would help. Pop recordings are full of various effects, but knowing that on track X the guitar is supposed to be far to the left, or whatever, would be good. If I had a few such references I'd feel more confident in my results. Any suggestions for recordings that provide this kind of information?

Thanks for any help.
Opus 3 has some recordings on CD which originated on LP called "Depth of Image" and "Timbre" which are outstanding IMHO for your purposes. Opus 3 was selling a CD set over the internet. These recordings come with a description of what each track will reveal (or should if your system is set up right). The tracks are all simple mic recordings of vocal, instrumentals, small groups, choral etc, and use classical, jazz, and pop music, albeit with a Swedish accent. I personally prefer these by far over other available 'test' recordings. FWIW.
I've used Opus 3 stuff and it is ideal. With CD in repeat mode, you can quickly train your ear to detect 'better'.
Magister check this link out. I have used a very similar speaker setup. The master set up is the best thing you can do for better sound and its free. IMO
Thanks for both suggestions!
I am not joking when I post this, but it really should be the most listened to or favorite recording in your collection. I find it is the easiest way to tune a room, especially if you have adjustable components, because in your mind you have a sound you most identify with. I myself have a personal favorite, Paul Kelly's May 1992, which has a great soundstage, silence and decay, and pure, isolated instruments. I also use Radiohead's Amnesiac, which has many moody and difficult to reproduce tracks. Just my POV. I think a hi fi system comes alive when you know of a recording for a decade, it has been a soundtrack to your life, and it comes alive into another dimension or nuance. That is what keeps me loving music, not some analytical CD that proposes that it can recreate a "depth of image."