Daisy Chain does not work with Quadro FX 880 M, 2 x Dell U2415 on Win-7

Hello everybody This is my first attempt to ask "the internet" about an IT topic. I've chosen this group, although it might me not exactly appropriate... I do have the following setup: Elitebook 8540w workstation (my old bby!) running with Quadro FX 880 M on Win-7, i7 M620 64-Bit. Now I wanted to expand my screen with 2 extra Dell U2415 screens in daisy chain setup using twice DP to DP cables. But after trying all hacks and tricks I knew and could search for, I only manage to mirror the two screens. Meaning, that I can disable the Laptop screen by closing, Dell 1 is properly showing main desk screen instead, but Dell 2 is just mirroring 100 %. I already followed the advice to enable DP 1.2 on Dell 1 and to disable DP 1.2 on Dell 2. Still mirroring. Does anybody have an idea if it is even posible with my HW? Thank you so much and best regards!