Never mind... I just realized you need to add the -depth switch to convert all of the various arrays of objects down the hierarchy. I used ConvertTo-Json -depth 10 and got what I needed.
What is the best approach to build a hardware profile of a standalone C-series? I'm using the IMC powertool "Get-ImcRackUnit" cmdlet and it might be missing some of the pcie adapters (I need to test further if this is an HCL or Powertool issue).