That text is misleading, probably bad translation.
Stardust slot only accepts stardust crystal of proper color and shape (sliver, shard, gem)
Safeguard slot only accepts proper Safeguard Stardust.
You however can use +7 and higher enhanced gear (magic or rare doesn't matter) to fill in Relic slots thus increasing your chance of successful enhancement.
Even +7 gear gives you better success chance boost than regular Narak Relic or Blessed Narak relic but it's quite expensive to use enhanced gear instead of naraks.