Hardware recomendations?

PCW wrote:

The 7I77 analog outputs have a ~2 KHz bandwidth so should be OK unless you are talking
about really high servo speeds (say >3600 RPM on a 4 pole motor = > 120 Hz sine waves)

Note that both the 7I65 and 7I77 encoder inputs are multiplexed inputs so reading the GPIO
bits will just return bit-hash since the GPIO pins are a combintation of both the even and odd
encoder input pins.

The demuxed A,B,I pins are available from the firmware but the hostmot2 driver does not present them to HAL

The differential Hall signals can likely be read using single ended inputs (like the 7I77 inputs) or OPTO inputs (like a 7I37) as they do not need much speed

another option is to ignore the Halls and use index rotor alignment

Are there other options that could raise this speed limit to oh say 6000 RPM?

What would be my limits be with an 8i20 setup?

6000 RPM should be OK (200 Hz with a 4 pole motor) you would just lose
some torque because of the phase lag. The 7I77 has a maximum delay in the order of 250 usec
at 200 Hz this represents about 18 degrees of phase lag which represents less than 5%
loss of torque

Note that for torque mode drives and for better commutation you are likely going to need to
run the servo thread at 2 to 4 KHz with either 7I77s/analog commutation or 8I20s

What about using a 7i20 with a 7i52, two 7i42s and four 8i20s? Would that all work together?

it should (assuming you mean 5I20 instead of 7I20)
You still dont have differential Hall sensing with this however
Can you check the levels on the hall pins? like I said before these may be readable single ended

Yes sorry I mis-typed the 5i20.

And I was wrong about the differential signal for the Halls. The sheet the motor manufacturer sent me was for a newer motor. that has 6 wires from the Hall sensors, The halls on these are single ended after all.