When I got the board I tried to find the lane allocations via HWInfo, you can find my result
here.
For the M.2 ports it looks like this...
M.2 Slots (12 CPU lanes in total / 4 via PCH)
M2_1 Onboard (between PCIEX16_2 and PCIEX16_3) -> PCI Express 3.0 4x via PCH
M2_2 Onboard (between PCIEX16_1 and PCIEX16_2) -> PCI Express 3.0 4x via CPU
DIMM.2_1 Module -> PCI Express 3.0 4x via CPU
DIMM.2_2 Module -> PCI Express 3.0 4x via CPU
Have no U.2 to check how those are connected, but according to the manual it shares the lanes with M.2_2 connected to the CPU.
PS Before you cut your Titan RTX, give it to me. I could use this beast for GPU rendering
🙂 There are PCIe 4x riser cables on the market! So I would go this way or use another sound card (USB or just onboard).