According to the DX9 docs the values below are the only valid ones for BackBuffer and Display.
A2R10G10B10 / Backbuffer & Display(Fullscreen only)
A8R8G8B8 / Backbuffer
X8R8G8B8 / Backbuffer & Display
A1R5G5B5 / Backbuffer
X1R5G5B5 / Backbuffer & Display
R5G6B5 / Backbuffer & Display
A2R10G10B10 / Backbuffer & Display(Fullscreen only)
A8R8G8B8 / Backbuffer
X8R8G8B8 / Backbuffer & Display
A1R5G5B5 / Backbuffer
X1R5G5B5 / Backbuffer & Display
R5G6B5 / Backbuffer & Display