Yes, you can use NI-9881 with cRIO-906x chassis.
You can follow the steps below.
1. Add NI-9881 under
Real-Time Scan Resources2. Add C-Series Modules, which you wish to use, under
FPGA Target3. Make sure that Chassis is in
LabVIEW FPGA Interface ModeRight Click
Chassis(cRIO-906x) >> Property >>LabVIEW FPGA Interface4. Compile the empty.vi under
FPGA TargetPlease refer
Getting Started with CompactRIO for the details.
6. Deploy
Right Click
Chassis(cRIO-906x) >> Deploy7. Now you can see NI-9881 in NI-MAX