Any other way to tell?
Yes. The difference between a 'normal' ng and a dl is that the last one is sold without disks. (dl for diskless). To make it possible to initialize a harddisk without hassle, it has firmware in flash. The ng version has only 1MiB flash (only containing a bootloader), the dl has 1GiB. On the PCB photo here
you see a non-dl PCB. The dl has a flash chip on u44, on top-right.
Yes, disks spin up after about 30 seconds.
For a non-dl that is far to late. The flash only contains a bootloader, so it has to read it's kernel from harddisk. The disk spins up within 5 seconds. I don't know if the dl will first try to read it's kernel from harddisk, or if it will always boot from flash. If it boots from flash 30 seconds might be OK.
Yes USB stick LED does flash after about 40 seconds, but then no much activity. So USB port and stick seem good.
I don't know if the same imager stick can be used for both the dl and ng. The firmware searches for a specific directory (\emctools\<hardware-tag>\, or something like that). When that directory isn't found, the stick is further ignored.
Where can I find the instructions (pins or header to connect, etc.) to connect the serial wires for console access to the NAS?
The pinning for the ix2-ng/dl is on the PCB page, the pinning for the ix2-200 is here
. Always connect only RX, TX and ground. The Vcc pin is only for reference for some specific TTL devices.