Actually, to be more precise, the video signal path is:
2) Monoprice 4:2 matrix HDMI switch
3) Sony HT-CT550W receiver (split for audio here)
4) Monoprice 4:1 HDMI switch
5) Epson 8345 projector
The reason for the matrix switch (step 2) is because I've got more HDMI inputs (PS3, 360, PC, cable) than the Sony receiver has HDMI inputs (3), and also because the matrix switch lets me display on my Dell U2711 LCD monitor as desired.
The reason for the second switch (step 4) is because I need a 25+ foot long HDMI cable, but the best I have at the moments is two 10 foot cables; that switch is acting as an extender :P
If you want, when I get home tonight I can do the RB3 video calibration test with the 360 directly connected to the projector with absolutely nothing in between.
In my case, though, particularly for rhythm games, it's better to have ~40ms video and ~40ms audio lag, rather than ~20ms video and ~20ms audio. The fact that they're both almost the same is desirable. After doing that benchmark, I went and beat a bunch of my high scores in the game, despite having not touched the guitar in months, so I'd say that either the projector lag is A-OK, or Rockband's latency compensation works well