Most sources seem to agree that it's best to germinate seeds in unfertilized seed starting mix. There's a split between barren soil mix vs. compost-added mix. Either way, most seedlings except those identified as "does not transplant well" or "does not like roots disturbed" benefit from being moved to a slightly richer mix when a set of true leaves (2nd set of leaves, first being seed leaves) have grown out (Use the seed leaves -- they're expendable
-- or cradle the root ball to transplant them -- DON'T hold the stem and don't hold the true leaves).
As for the coneflower, many wildflower seeds require cold stratification (a period of storage in cold -- some in moist environement, others dry). I'm pretty sure purple coneflower is one of them. I've never tried those, but usually, the recommendation is to refrigerate the seeds in moistened sterile medium like sand, vermiculite, or perlite in a zip bag or tightly sealed snap lid container for the recommended period, then plant the seeds.
Another possible reason for seeds not sprouting is that they were planted too deep. Seeds should only be covered by their thickness. Tiny seeds or seeds like lettuce only needs a sprinkling of sand to keep them from being washed away, and, in fact, germinates better in light.
Good luck with your rare seeds!