If I’m picturing this correctly your speakers are against the wall 4 feet away from where your computer desk and you are located. If that’s correct then as long as there is a direct line-of-sight between both speakers and both your ears then the monitor is not blocking any of the sound radiating directly at you. It will, however, redirect some of the sound waves at you that would otherwise have passed by. This will effect the imaging and possibly colour the sound. However, I imagine having your speakers in the bookshelves will do more to colour the sound and effect the imaging than the monitor.
You could increase the relative separation between the speakers to you by moving your desk closer to the wall the speakers are on or moving the speakers off the wall and closer to you or moving the speakers farther apart. You could then play around with toe-in to see what produces the best overall soundstage.
If buying a large flat panel in in your near future you could get one and hand it on the wall between the speakers and keep your desk where it is. I use my HDTV as my primary computer monitor and it’s great.
Cheers,
Dean
