Dell R510 with S100 and (4) cabled 4TB drives - Needing to upgrade raid controller

Hello,

 Helping a client try to get old of their legacy R510 servers setup to handle their offsite backups.

It is an R510 with the basic S100 controller and has (4) cabled hard drives currently (all 4TB).

All drives plus into sata plugs directly on the motherboard. There isn't any hotswap backplane to speak of.  I'm needing to be able to do at least Raid-5 and have it support the full drive space in the Raid Array (12TB, not get cut at the 2TB limit).  We never deal with S100/cabled servers so I wanted to reach out to see if anyone could give guidance on what part(s) would be needed to make this happen. Not trying to get the drives to be hotswap (cabled is fine) but need to know what controller (6i, h710, etc..) would be needed and if any new cables would be needed as well since these currently plug directly into the Sata1-4 on the motherboard.  Thanks for any input you might have.

Matt