Amaryllis allows me to "attempt to recharge a spell in your discard pile." Do I use the text value at the bottom of the spell that used to be the Recharge box in Runelords (ex 8 on Frost Ray)? I was told that recharging from the discard pile uses the Check to Acquire value instead (ex 6 on Frost Ray). Where in the rulebook does it say?
I don't see anything in the rulebook. I'd say you use the check that relates to recharging it when you would have played it (i.e. the check that previously was in the recharge box).
As usual I agree with Hawk. Unless instructed otherwise (and it's not the case), you apply the standard recharge conditions (usually a Divine or Arcane check for Spells) as per the card.
Unofficially:
Pretend you just played the spell. Do what it says afterward.