Aspect Ratio Scripting

I am trying to author a dvd with 16:9 and 4:3 letterbox video & menus. I want the DVD to check the player to see whether the aspect ratio is set to 4:3 or 16:9.

This works in all of the set top DVD players I have tried it in(presuming the player and monitor are set up correctly.)

I have a prescript on my first play(the 16:9 menu)which contains these three lines.
mov Aspect check, SPRM 14
div Aspect check, 1024
Jump 4:3 Main Menu if (Aspect check <3)

The issues start when I put the DVD in a computer.
In Mac DVD player the 16:9 menu is always played.
In a PC(3 different softwares) the 4:3 menu is always played. I have tried 16:9 studio releases and they display correctly in the same machines.

Does anyone know if software players have SPRMs like a set top unit to check?
I am currently only using the Aspect ratio portion SPRM 14(bits 10-13)to check what the player is set to. I know that SPRM 14 bits 8&9 show display mode but shouldn't the Aspect ratio check be enough?

grateful for any suggestions,
Brad