Because i also have an old gaming PC, used as home lab with proxmox and truenas VM, i simply bought cheap PCI extension cards and put all my existing 4tb M2 inside and created a new 6 x M2 pool in Truenas.
The mother board is X570-AORUS-ULTRA (5 pci slots + 3 m2 slots + 6 sats slots) with 3950x CPU and 128gb RAM.
I used all available PCI slots/lanes as follows :
-PCI x16 : 4 × 4tb M2 via PCI to M2 extension card (bifurcated as pci 4×4, for 6 x M2 truenas pool)
-PCI x8 : not used because if used i loose 8 lanes on the PCI x16 slot (and loose 2 M2 slots)
-PCI x4 (the bottom slot on the mobo) : RTX 3070 graphics card (passthrough to linux mint proxmox VM for docker containers and plex, 20% GPU speed loss compared to 16x slot, not a problem for Plex and docker usage)
-PCI x1 : PCI to M2 extension card + M2 to 6 sata adapter (6 hard drives for truenas VM)
-PCI x1 : PCI to M2 extension card : 1 x M2 2tb drive for proxmox VMs storage
-2 M2 slots on the mother board used for 2 × 4tb M2 (for 6 x M2 truenas pool)
-1 M2 slot on the mother board used for 10gbe M2 ethernet card
With this setup i have :
-10gbe lan
-8 usable sata slots (6 via M2 and 2 on the mother board : some sata slots if used disable M2 slots because sata and M2 lanes are shared via PCI switch)
-7 x M2 slots (2 on mobo + 5 via PCI extension cards) : 6 x M2 truenas pool + 1 x M2 for proxmox VM storage
-RTX 3070 GPU passthrough to linux Mint VM
Price for PCI extension cards (Amazon France) :
-PCIx1 to 1 M2 : 6€ (bought 2 of them)
-PCIx16 to 4 M2 : 40€ (motherboard bios has to have 4×4 bifurcation option for pci x16 slot to use this type of card)
-M2 to 6 sata : 25€
-M2 to 10gbe LAN : 120€
-M2 extender : 20€
You could even have more PCI/M2 if you use Proart Creator motherboard witch already has 10gbe port, so one more PCI slot would be available compared to my setup. This would lead to 10gbe + 8 sata + 8 M2 homelab+nas with CPU+GPU+RAM of your choice :)
In Truenas VM i have :
-one pool of 3 mirrors of 2 x (16tb and 18tb) disks for 50tb usable capacity and maximum speed and IO
-one pool of 2 raidz1 vdevs 3 wide (6 × 4tb (3.6tb usable) crucial T500 M2) for total usable 13.7tb (30% capacity loss but 2 parallel data channels/streams because 2 vdevs)
Both pools saturate 10gbe lan connexion.
The setup is compute superior (cpu+gpu+10gbe lan+ram) to all M2 Nases available,
but consumes 200-500 watts and costs less if you already have an unused PC laying somewhere.
