Nick,
These are basically the same as the original HX300 servo amps. The circuits are moded to work with the 8in OB subs instead of the 12in OB subs.
This time Danny redesigned the 8in sub woofer to be slightly higher impedance so the amp could drive 4x8in instead of just 3.
The other difference is extending the LF response to 30Hz and using the dspNexus 2x8 to control the low frequency extension. It was around 40Hz before. Will have to wait until the servo drivers are mounted in the H-Frames to adjust the response so they do not bottom.