Yes I did try several position, and put it up and vertically.
It's like there is a high cut somewhere, or the tweeter off, something like that.
Anyway, I read in a lot of forums that the HR FRFR 108 or 112 were the worst sound experience for other guitarists than me, thus I'm not sure my unit has a problem.
Connected to normal music it sounds great. It's just not designed to sound like a guitar amp, that's all ;)