Problems with two grphics cards X sevrer initialization at startup

[Snowhog]

Hello all,
first i want to thank everyone for helping me in the past! ;-)

Emphasis added by Snowhog.

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Hello all,
first i want to thank everyone for helping me in the past! ;-)
But now i can't find a proper working solution somewhere on the forums.
Problem is I have a pc with two graphics cards. Main card is a Sapphire RX580 and the second one is an old Nvidia tesla M2050 accelerator. Since i want to use the Tesla for my cuda programming stuff i had to install the latest nvidia driver and this is where the pain starts.
At startup the x server goes on the Tesla card as main card which is no fun without any monitor connections on the board. ;-)
My workaround at the moment is to go to a console via ctrl+alt+F1 move the xorg.conf to a different xorg.conf then start the xserver from the console. This is quite annoying to be honest. I tried modifying xorg.conf but the Device PCI:5@0:0:0 (amd is on pci 1) always keeps on to be the device it will start with. Which script do I have to modify to force it starting on my AMD card?

I need the RX for gaming on Windows. ;-) So when there is no nice solution for this I'll have to get a second scrap metal pc for the programming stuff with two nvidia cards installed there was never a problem on this mainboard and cpu.

Thanks in advance!
Greetings form germany,
Christoph

lspci says this:

00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD/ATI] RD9x0/RX980 Host Bridge (rev 02)
00:00.2 IOMMU: Advanced Micro Devices, Inc. [AMD/ATI] RD890S/RD990 I/O Memory Management Unit (IOMMU)
00:02.0 PCI bridge: Advanced Micro Devices, Inc. [AMD/ATI] RD890/RD9x0/RX980 PCI to PCI bridge (PCI Express GFX port 0)
00:04.0 PCI bridge: Advanced Micro Devices, Inc. [AMD/ATI] RD890/RD9x0/RX980 PCI to PCI bridge (PCI Express GPP Port 0)
00:09.0 PCI bridge: Advanced Micro Devices, Inc. [AMD/ATI] RD890/RD9x0/RX980 PCI to PCI bridge (PCI Express GPP Port 4)
00:11.0 SATA controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 SATA Controller [AHCI mode] (rev 40)
00:12.0 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI0 Controller
00:12.2 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB EHCI Controller
00:13.0 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI0 Controller
00:13.2 USB controller: Advanced Micro Devices, Inc.

[AMD/ATI] SB7x0/SB8x0/SB9x0 USB EHCI Controller
00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD/ATI] SBx00 SMBus Controller (rev 42)
00:14.2 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] SBx00 Azalia (Intel HDA) (rev 40)
00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 LPC host controller (rev 40)
00:14.4 PCI bridge: Advanced Micro Devices, Inc. [AMD/ATI] SBx00 PCI to PCI Bridge (rev 40)
00:14.5 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI2 Controller
00:15.0 PCI bridge: Advanced Micro Devices, Inc. [AMD/ATI] SB700/SB800/SB900 PCI to PCI bridge (PCIE port 0)
00:16.0 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI0 Controller
00:16.2 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB EHCI Controller
00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 15h Processor Function 0
00:18.1 Host bridge: Advanced Micro Devices, Inc.

[AMD] Family 15h Processor Function 1
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 15h Processor Function 2
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 15h Processor Function 3
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 15h Processor Function 4
00:18.5 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 15h Processor Function 5
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 470/480] (rev e7)
01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Device aaf0
02:00.0 USB controller: VIA Technologies, Inc. VL805 USB 3.0 Host Controller (rev 01)
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 0c)
05:00.0 3D controller: NVIDIA Corporation GF100GL [Tesla T20 Processor] (rev a3)
05:00.1 Audio device: NVIDIA Corporation GF100 High Definition Audio Controller (rev a1)