5.5 million PS3s sold

[Dolla Dolla]

The 5.5 million cites number "sold" by Sony from their Annual report (fiscal year 2006), just like the 5.84 million is the number used by Nintendo.

From your second source, ssj12:
"In its annual report, Sony said it sold 5.5 million Playstation 3 units in the fiscal year ended March 31 2007, despite having faced production yield problems for its blue semiconductor lasers that feature inside each machine."