Re: L22 as Horizon "stand"
I don't think it is a problem at all in terms of sound quality, as long as the Horizon is pulled to being flush or slightly hanging off of the front of the L22. My seated ear height is about 42 inches, so if I were in your case I would just orient the L22 so that it is upright and then place the horizon on top. But that requires and acoustically transparent projector screen, or a display mounted uncomfortably high.
That is crazy that the Horizon is that wide. It doesn't look like it in the photo. It will look this imposing stack of speakers. :) I think it would look cool though.