Somehow I ended with only 3 of the keys needed to buy soul boosts, despite having many keys and thousands of lost souls in my inventory. Not sure if that was meant to be the conversion rate or not...
Go to Inventory.Sell each of your remaining Hades Keys (to get new Skeleton Keys instead).Then go to Crystals pages (NOT the Store pages) and buy Souled Out Crystals w/ the Skeleton Keys (max 15 crystals, which equals max leftover of 30 old Hades Keys)(Kabam still hasn’t commented about missing out on not being able to use remaining Lost Souls for these, as game Mail in theory said should have been possible).