VBA (Excel), with an amazing 322 bytes
Yeah, and I LOVE hexadecimal. (There's no sarcasm font yet, so I'm using italics for now) I'll add comments if someone wants, but I think it's self explanatory.
Sub b(s)
For Each c In Split(Replace(s,"D",""),"B")
Select Case c
Case"I"
c=0
Case"A"
c=1
Case"O"
c=2
Case"U"
c=3
Case"II"
c=4
Case"IA"
c=5
Case"IO"
c=6
Case"IU"
c=7
Case"AI"
c=8
Case"AA"
c=9
Case"AO"
c="a"
Case"AU"
c="b"
Case"OI"
c="c"
Case"OA"
c="d"
Case"OO"
c="e"
Case"OU"
c="f"
End Select
d=d &c
If Len(d)=2Then
E=E &Chr("&h"&d)
d=""
EndIf
Next
Debug.?E
End Sub