Thank you very much. I found the problem.
With:
config="sserial_port_0=00000000"
the 7I84U boards are detected correctly.
At the moment I have only two 7I84U boards powered with 28V, and LinuxCNC detects both of them on channels 5 and 7:
hm2_7i97.0.7i84.0.5
hm2_7i97.0.7i84.0.7
So the 7I97T, 7I74, firmware, adapter and DB25 cable are all working correctly.
The main issue was that I was previously using:
config="sserial_port_0=x0xxxxxx"
and I had also misunderstood the physical channel numbering on the 7I74.
I will now power the other two 7I84U boards and test all four.
Thank you again for your help.
