I tried a similar experiment with Infinity Primus 150's (which I currently employ as speakers in the living room being fed by a Yamaha HTR-N5060).
I couldnt consistently tell the difference between vertical or horizontal placement. The only change I could consistently pick out was when the speaker was oriented upside down vs right side up in vertical placement.
Try this with a capable partner (and a few beer). Dont be shy and get the blindfold out. With the right person, Beer, blindfolds and music makes for a fun hour....
