I have a question with Soraka and Atakhan, can Soraka save units optionally killed for Atakhan AND Atakhan still receive the discounted cost?

Yes, you can save the unit killed for the additional cost of playing Atakhan using Soraka, Wanderer, and you will still successfully pay the cost to receive the cost reduction.

Why this works:

1. Cost Payment: When you play Atakhan, you choose to kill a friendly unit as an optional additional cost (as permitted by his card text).
2. Replacement Effect: Soraka, Wanderer has a replacement effect: "If another unit you control here would die, if it has less Might than me, instead heal it, exhaust it, and recall it."
3. Rule 357.2.a: According to the core rules of Riftbound, "Costs that are replaced with other events by replacement effects are still considered paid."
4. Interaction: Because Soraka’s replacement effect intercedes to save the unit from dying, the "Kill" event is replaced by "heal, exhaust, and recall." Even though the unit does not actually die, the cost is still considered paid for the purposes of the card you are playing.

This interaction is consistent with RiftJudge FAQ #9045 and FAQ #374, which specifically confirm that killing a unit for an equip/play cost while using Soraka to save it successfully fulfills the cost payment requirement.