5P33D

Hello everyone, Im using an Akitio Thunder2 with the Late 2013 15" Macbook Retina featuring an gt750m dGPU and an 2,3Ghz i7 with an Lepa Maxbronn B1000M Powering the Akitio (12v and ground soldert to the barrelplug as well as to the PCIE Socket). I tried using a MSI Lightning HD7970 as eGPU. While under OSX the card seems to work using modified kexts(<key>IOPCITunnelCompatible</key><true/>) (listed in system report, display settings as hd 7xxx 3072MB and in apps as a Tahiti XT prototype also the display connected to it delivering output) the performance in Benchmarks and Games was EXACTLY the same as when using the 750m so i think that the image is rendered by the dGPU and not on the eGPU (yes output is on the display connected to the 7970). When using windows (no mater if 7 or 8.1) it gets even worse the dGPU disables itself completely on startup (reporting it has been disabled because of an error in the device manager) while the eGPU is using software rendering and showing an error35 in the device manager. The problems mentioned above happened using any kind of ATI/AMD gpu (Tested HD4670, HD6990 and HD7970) but not when using an NVIDIA gpu while testing (8500GT, 8600GTS and 9300) no errors occurred all of them working perfectly in OSX as well as in windows. I hope someone of you has an Idea how to fix this. If not, should i consider buying a used GTX580 which seems to me having the best power/€ ratio of all somewhat decent Nvidia chips costing about 80€ on ebay? Thanks in advance, 5P33D