The DVA I was able to find on the web looks to be a standard Cation water softener using salt and the resin can be recharged with sodium chloride or potassium chloride if you desire. Looks like a bigger version of the Cation cartridge I just ordered to put under my sink along with a carbon filter.
The Claris water softener system uses a Hydrogen Ion exchange and the cartridges are not rechargeable.
I can't explain why the Hydrogen Ion exchange is better then the Sodium or Potassium Ion exchange, but the Claris represents the latest thing and is reputed to be excellent for espresso.
Wikipedia seems to hint that there are some Hydrogen based systems that can be recharged... with Hydrochloric Acid. Doesn't sound fun.