Hey Woochifer, nice to see another Shiva in the mix
Your sub looks great, very smooth. It's funny you mentioned that boominess at other positions, I noticed it earlier today. It was driving me nuts, I'm going to move my sub to the front corner so I can use the room gain to add to the lower bass instead of using the boost and re-equalize. For a sealed sub the shiva really impresses me in the low end.
I'm actually using a Yamaha HTR-5640, good guess

Maybe you can answer a question for me. My mains, center and rears are all set to "small". And bass output is set to "sub". Now does that mean all material below 90hz from all channels goes to my sub along with the LFE? Or is it just the LFE?
Just curious, I'm planning on adding a sub to the surround channels. I'm going to connect it using the subs speaker ins/outs. How do I go about testing it so I can get it level with the speakers? Connecting it to the BFD would be too difficult so I'm going t leave it out.
I was also thinking of putting the second sub on my center channel instead of the rear, since the center channel has a great deal of material in a movie.
Thanks.