Never heard of CRS, but a quick google search indicates it's a "blend of acids".
Boiling water removes temporary hardness (e.g., bicarbonates) by precipitation. A lot of energy is required/wasted to boil water.
Acids remove both temporary hardness and permanent hardness (to a lesser degree) by exchanging hydrogen ions. The downside is, after the ion exchange, you'll increase the concentration of ions on the right side of the reaction (e.g., SO4, PO4, etc.) which will affect the taste after a certain threshold. Commercial breweries that are cursed with hard water tend to use acids because it's inexpensive.
Another option is to blend tap water with RO water to dilute the temporary hardness. You'll likely need to add back permanent hardness after the dilution, though. Many homebrewers use this approach.
