Triple 3870 Crossfire

So far I have 2 ati 3870s crossfired and I just ordered a third one so that I can triple crossfire them. For my first question, I have an Ultra x2 750 watt power supply and I wanted to know if this would be enough to powers three 3870s. Also it only has two 6 pin power connectors so I had to order a Y cable so that I can connect all three cards. I also ordered a molex 4 pin to pcie 6pin adapter just in case. Anyway, Do you think the Y cable or adapter will work to power these cards? I have heard that amperage can be an issue with Y cables. I don't know if it matter but the power supply has two 12v rails @ 25 amps each. Will this work or do I have to get a new power supply? I'd really appreciate any input on the situation. Thanks!
My system specs:
Asus m3a32 mvp deluxe
AMD Phenom 2 940
Six Gigs Muskin ram @1066 mhs
2 Visiontek Radeon 3870 HD's(soon to be three)
250 Gig Seagate Hard Drive
2 DVD burners
Ultra x2 750 Power Supply