Migrating from X-RAID2 single redundancy to Dual redundancy

I have two Pro Pioneer Systems that need to be upgraded this month.

System 1:
4 x 2TB Samsung HD203WI drives
X-RAID2 (single redundancy)
RAIDiator 4.2.25

System 2:
6 x 1TB WD WD1002FBYS-01A6B0 drives
X-RAID2 (single redundancy)
RAIDiator 4.2.11

My goal is to replace all disks and migrate to 4 x 4TB drives using RAID 6 dual-redundancy in both systems.

What is the recommended expansion procedure for each system?

System 1 has two open bays and gives me the option to use the next added disk for dual-redundancy. Should I add a new dual-redundant disk first, then start replacing existing disks? And would that require 5 disks final instead of 4? I'd like to keep it to four disks total and avoid a factory reset on this system if possible.

System 2 has all bays full already I assume I need to factory reset to get dual-redundancy, correct?

Both systems have just under 4TB of data and will be fully backed up before we do anything.

Any advise and suggestions on how to best proceed?

Thanks!