It's funny that your problem is a dull sounding room; most rooms are too bright! I think that what you're hearing, though, is two things:
1. The loudspeakers are not decoupled from your desktop and the vibrations are adding audible distortions to their sound. I had the same problem with my monitors. I didn't use Auralex, but I
did put Black Diamond Racing pods under each loudspeaker. (BDR makes great products, but they are hella expensive)
2. You are definitely going to have some issues associated with that bare corner between the loudspeakers. You should get a corner trap in there. Actually, most anything that will break up the sound waves will be a vast improvement -- tapestry, rolled up duvet, shelves with books on 'em, a couple of Auralex panels hot glued to foamcore, etc etc. I have a quarter round piece from Room Tunes in my corner; my setup is almost identical to yours in terms of desktop (corner piece).
Sorry for the cr@ppy webcam pic:
