Mr Khan said:

So what are O, P, R, S1, and S2?

Nothing yet... but there are some guesses.

More realiable

X: Display controller and UVD
Y: Audio DSP
V: Unknown but every Radeon have this part

In discussion

D: ARM core?
U1, U2, W1, W2: maybe fixed functions?

Marcan said too the he thinks the Wii GPU in into this chip too.