|"I always put it under my desk with a raised platform underneath"|
You didn't mention a raised paltform in the OP.
"The gallery shows something like three bays in the upper portion (all concealed) and apparently nothing in the lower part"
Correct. And if you looked at ALL the pictures, you'd see that the 2nd bay has a door which hides the audio ports & USB ports. There is NOTHING at the bottom. This is all shown very clearly in the pictures.
"If you own it can you tell me where they actually are?"
I would never own a Dell.