Hmm... I often have people discuss sermons with me, even up to weeks later. They listen, quite a few take a copy of the text or read it when I post it on my blog, they reflect, pray, and continue the discussion. My impression is not that their engagement with the material is passive.
I mean, sure, some are probably sitting there daydreaming. But some people would be doing that no matter what.
I've done discussion-style preaching and my experience is that it works less well the larger the group gets. Once you're beyond a dozen or so people relatively few tend to contribute anyway, and the discussion gets dominated by the more forthright personalities (which isn't good either).
I don't think the format of our services is necessarily a problem. "Body ministry" should happen throughout the week.