Foxy - brilliant, well done - so far.
On my Jap Modchipped scph 15000 it needed only the following buttons pressed together:
L1,L2,R1,R2,UP - much easier than your original recommendation.
Of course it didn't actually work. It got me to the Jap DVD menu which, thanks to the UK manual I got off a UK PS2, I managed to decipher-ish. When I pressed the PLAY key on the menu, the PS2 locked up with the PLAY legend on the top rhc. For now I'll give the benefit of the doubt to the PS2 because the Black Adder DVD was bought in France. I'll post the outcome in a couple of days when I've got hold of a pukka UK DVD. If it works, my hat is off to Foxy. If not, perhaps someone can tell me what's going on.