Have eight channels of 8k in my console (rest 4k)
The routing on the 8k run A-D, a-d, then 1-24, so any 4k channel you'd have to hit channel 9 to get bus 1 on the 8k.
So, I plan better, and not having access to bus 1-8 on the 8k channels and then everything shifted by 8 doesn't bother me... but it could be a nightmare for someone else.
Also, the 8k has a route button, rather than float.. I'll try and find the channel signal flow for this.
You could modify all the 8k to be 4k channels, it's all one extra (ADCD) board and cut traces.. my intension was to do this.. but not had the time as yet :-))