Sorry but I would go for neither one.
First off, unless my math is off your room seems a bit on the small side for either of these. Both of those horns are fairly wide dispersion and given the size of the cabinets they will have to be placed closely together, which will make the channel separation worse.
I've heard the 3677, and I don't think you will be impressed. This was a design from the old Dolby SR days of matrix encoded optical sound. The high frequencies roll-off considerably from 12-20k. Optical soundtracks were not capable of much very high frequency content, so the design of this cabinet is to sound loud but not great.
I have not heard the 3722N, but again it is going to pose more problems. It's a larger cabinet and horn, so again spacing will be limited. Also, it is a 4 ohm load. I'd make VERY sure your Denon can handle it, as most AVRs are not capable of doing 4 ohms. Also, you will be severely underpowered, so you will have to watch your levels on playback. The design is newer than the 3677, and will be more capable of reproducing a modern digital soundtrack, but I just think there are way better options out there for the money. Now, if you were talking about building a 20 seat theater, I would say go for it, but 3000 cu ft is a bit small. Did you maybe mean 3000 sq ft instead?
Hope that helps, sorry if I rain on your parade a tad.