Why towers? I have a set of towers and if I could it all over again I would go with bookshelves and a good sub. Towers are great, they're also big, an eye sore, big, always in the way, and big... Get the picture?
Do you have a budget in mind?
What type of display do you want ? projection/plasma/LCD
You have a few issues working against you.
1. Ambient light from that massive window. You're either going to need to tame it with curtains or get a very bright flat screen. Most likely both.
Motorized curtains or blackouts would give a great 'coolness' effect to the room and also cost big $$$.
2. Sound. It's going to carry throughout your entire house based on all the pictures I just clicked through.
A simple solution would be to get the largest flat screen you can and a mount that supports LCRs (Peerless MSA-301) . Buy something similar to Mythos XTR-50
slim speakers. Mount the TV and LCRs together in that TV hole. You could get a mount that extends so you can push the tv back in or pull it out. That may help with ambient light issues and give you a great method to tuck it away.
For surrounds. I would go with in-ceiling surrounds and put them behind your two cushion couch, aiming at the couch. Don't get surrounds that point straight down, you want the angled type. Like these.
BTW: Your basement looks like a great future HT project.