Would you consider 3 Triton Twos for LCR speakers (behind an AT screen) too much? I am concerned that having effectively 3 subwoofer sections might be excessive.

No problem - and you can always direct the low bass (below 80Hz) from the center channel Triton to the L/R if you wanted to limit the number of low bass output sources in the room. I've heard this setup in a good size room and it sounded spectacular.

I am glad to hear that 3 Triton two's sounded good for the left right and center channels. But did the set up that you cited actually the cut the base to the center channel or were they all running unrestricted?
in any case can you tell me if there could be any advantage to having a subwoofer with this setup in a room that is 13 feet by 28 feet?

All were running full range, but in a MUCH bigger room (more like 30' x 50'.

The Triton Two produces significant bass down to about the low 20's (the pair I have in my room produce room flat bass to about 24Hz) and produce a TON of bass in my average size listening room. However, it has been shown that the LFE channel in some movies has information all the way down to 10Hz (below what you can hear, but still something you can feel). If you want to reproduce this information (regardless of room size - although the room may limit the actual extension), you would need a separate LFE channel subwoofer that is capable of significant sub-20 Hz output.