gitSehT, thanks for the comments. looking forward to your ht progress as well.
1.) the walls were made short to avoid any contact with the floor joists. this is to minimize vibrations and sound transmission throughout the house. i used rsic dc04 clips to attach the walls to the floor joists. they are decoupling brackets.
2.) yes, both the stage and riser are secured to the floor. what i did was cut a few pieces of 2' long 2x4, screwed it into the concrete floor and then nailed the stage/riser to it. a few pieces at random spots for each keeps them attached. i know many here suggested simply to leave it floating, but i like to make things secure. by the way, i used a rubber dampener material called iso-sill from a local soundproofing company. i lined the bottom of all the riser/stage joists. so technically, no wood is touching the concrete. this method is similar to using u-boat floor isolators. i also did this with the 2x4 pieces that were screwed into the floor. (btw, you can kinda see them in the sub cavity pic and the stage with completed curve pic)
3.) to be honest, im not really sure yet. worse comes to worse, i will build an ib in that space, or i could simply build a box that is the exact size and have the woofers firing forward into the room.
4.) ha, to be honest, that took me about an hour of work. never used sketchup before, but i watched a few tutorial videos on youtube and voila! its very easy once you see how to do it.
5.) i did that design a while ago so i don't remember exactly where i got them from, but i do remember downloading it from a link either from here or searched on google.
6.) no worries, i charge admission.