I have the 800v4. I know the amp is definitely different than the original that Tom Cumberland engineered. Besides the continously adjustable phase control and the lack of a USB port, I don't know what all the differences are. Andrew also got rid of the room gain knob which was nothing but confusing for me. I bet the DSP code is better (lower distortion, etc), the firmware and hardware more robust and reliable and it just plain sounds better than the original. I also think the drivers and cabinet are much improved. I am taking mine to my grave. I lived with the curse of the 600v2 for 11 years and thank Ian that a year ago he let me trade in for an 800v4. The v4 DSP subs are simply amazing. You might want to consider trading yours in for a 600 instead of an 800 if cost is an issue.
Geez, that looks like a nice amp. Congrats! It's tough to make a call on what sounds best for cross-overs because it depends on room, ears and gear. I've found my system sounds best with the 160v4 and QS10HP at 40Hz and M5HP at 80Hz. My Onk's Audyssey XT32 found them all at 40Hz by the way.