You'll get deeper bass from the two π speakers. You probably saw this recent post, but if not, you might wanna read it. It was in response to a comparison between the little π's and single driver speakers.I really like the Fostex 206e and the little Adire HE10.1 is nice too. But I prefer two π speakers to either of them, and if not, I'd make a Fostex-based one π and an Eminence Beta based two π. Nice thing is that each of these speakers are available, so a guy has plenty of good choices. You really can't go wrong with any of them, especially when used with a system like you describe. Each is perfect for that system, and they all sound very good.
Having said all that, build a pair of two π towers and report back to us what you think. 'Cause I think you're right, it's a no-brainer.