7i97t with 7i84d connection problem

beside the traditional limit switch for x and z the mpg and step speed control   i need another  44 digital input and 27 digital  output  that means  2 7i84 
in the description of the 7i84 i see "The RS-422 interface at 2.5 MBaud is compatible with HostMot2s SSLBP smart serial interface which can support as many as 32 7i84 cards for a total of 1024 inputs and 512 outputs"  before you told me  the 7i97t suport only one 7i84 but you can use the  availabe  expantion port and one on the regular port  or both on de expantion port  ? thats not clear  to me 

is it a good idea  to use a separate plc to controle the lathe and let the  7i97 do the nc of the axe ?

Final update on the topic:
a replacement 7i84 just arrived and I connected it in the same way. With the new card all inputs and outputs are working properly. I can see the card in halshow and it just works