Migration from Synology 8-bay NAS to 6-bay NAS with expansion enclosure?

[freedo100]

Hi, Please can you help a noob.
I have an 8-bay Synology DS1815+ (out of warranty) which has failed to power on after a reload. I tested and tried new PSU - no blue light - no motherboard. So I'm resigned to get a replacement Synology NAS (I'm using SHR).
I've seen the excellent youtube vid comparing DS1621XS+ and DS3617XS.
In my DS1815+ I have 8 drives: 4x6TB, 2x4TB and 2x18TB WD181KRYZ Gold new drives). The config uses SHR - with two volumes (6 disks and 2 disks).
The questions I have:
I) Will I be able to migrate to a DS1621XS+ by first installing just 6 drives (one volume) and then slowly reducing the number of disks to enable to add second volume
ii) If not, will I be able to use a DS1621XS+ (6 bay) + expansion (DX517) to facilitate an initial migration to the new platform. I appreciate long term best not to have a volume split via eSATA.
iii) or am I forced to use an 8 or more bay chassis for the initial migration.
Really appreciate your help with this
:-)

[freedo100]

Hi. I upgraded from the 8-bay DS1815+ to the 6-bay DS1621XS+ combined with the expansin unit DX517.A very easy process :-) and the optional SSD cache works a treat with a couple of NVME cards added.