I really planned on using a FiiO E7/E9 combo for a pair of Beyerdynamic DT 990 Pro 250 Ohms version.
Would it be enough to pull out it's full potential?
I need results
What sources will you be plugging the dac/amp into?
Do you have a specific budget?
A E7 and E9 will be able to drive to DT990 250 ohms just fine.