Converting PowerEdge C6400 24-Bay with 4 C6525 from SATA/SAS to SATA/SAS/NVMe Backplane

I’m working on converting a Dell PowerEdge C6400 (24× 2.5”) chassis originally configured with SATA/SAS backplane to a SATA/SAS/NVMe-capable backplane, and I’d like to confirm the correct sled / motherboard requirements.

Original configuration:

• Chassis: PowerEdge C6400

• Original backplane: SATA/SAS only

• Nodes: 4× PowerEdge C6525

• C6525 motherboard PN: CN-04DK47-WS300-9B1-00LF-A02

• single SNAP I/O : CN-0MRCX4

• Riser 2 PN: CN-0M6PP0

• PCIe cable PN: CN-02XCDG

Upgrade performed:

• Backplane replaced with SATA/SAS/NVMe backplane kit

• Backplane PN: CN-0N9YVX

• Linking board assembly: MP84G

• NVMe cabling installed as per backplane kit

Current issue:

• System fails during POST with storage/PCIe-related errors

• Boot error reported:

  • HWC2003: The storage BP1 PCIe B0 cable is not connected, or is improperly connected

• iDRAC reports PCIe / storage cabling health errors

• NVMe bays (front slots 0–1) are not detected

• All backplane, linking board, and cables appear correct

Finding so far:
The installed C6525 motherboard (CN-04DK47) exposes only a single SNAP I/O PCIe connector per sled, while the NVMe backplane + MP84G configuration apparently requires dual SNAP I/O (two PCIe links per sled) to support 2× front NVMe drives.

Question:
Can anyone please confirm:

1. Whether the existing C6525 motherboard supports dual SNAP I/O for NVMe when used with the SATA/SAS/NVMe backplane in a PowerEdge C6400.

2. If supported, which SNAP I/O / PCIe cable part number is required to enable dual-link NVMe for the front NVMe bays.

Thanks in advance.  Looking to confirm the correct hardware path rather than guessing part numbers.