Hi all, who want to speed up your NAS to 2.5G,
after I tried a bit with my Synology DS620slim and USB-to-2.5GbE-adapters - quite promissing - and had to give back a not working Ugreen DSX4800, I got an exceptional quote for a Qnap TS-653D including 5x14TB seagate EXOSs, which I accepted, and which turned out to be kind of a bingo.
Because that Qnap, even if already some years old, has two native 2.5GbE ports, an intel J4125 SoC and a standard BIOS setting one able to boot from any EFI disk attached.
As the first, I plugged in a monitor at the HDMI port, a keyboard at one of the USB2 ports and my Ventoy multi ISO stick at an USB3 port and pressed F7 after the first beep. Amazingly the boot menu allowed me to boot from Ventoy stick quite normally, and I could run memtest86 with or without "+", gparted, and even HBCD PE (Win11) and a live Linux (elementary OS 
without any problems. Ok, with all QTS formatted drives plugged in there were not enough drive letters left for HBCD PE, and most of its tools were missing, but there was nothing keeping it from running basically. Funny enough. I actually had not thought, that a NAS hardware would run a full featured PC OS so completely at all.
By that first trials I had noticed, that the BIOS could not only boot from "QNAP OS" and my stick as "UEFI OS", but still from a "P0". So I installed OMV on a separate SSD, and plugged this into one bay ofter the other, until it was offered as "P0" in bay5 and as "P1" in bay6. With OMV ssd in bay6 I went to BIOS and set boot order accordingly, rebootet and - had OMV booting. Without having anything of original Qnap installation touched, except for the BIOS settings.
After this, I removed OMV ssd and booted QNAP OS again, saved the config, removed all disks and put an old but known good 500GB drive into bay1, to which I let install the actual Qnap software - just to set me able to check for later firmware updates, meaning espacially BIOS updates. For this, I just need to plug out all OMV drives, plug in the QTS drive, monitor and keyboard and let run QNAP OS again. If there is a new firmware update, I can do it, and then go back to OVM.
Maybe there is yet another way to add a ssd/nvme with OMV by using a ssd adapter card in the pcie slot of the TS-x53D. But this is not clear at the moment. Some folks say, it is, other say no chance except with (expensive) original Qnap adapters only. I will just try out and keep you informed.
Best regards