FiiO E7 is limited to about 50 mW into the ~62 ohms of the K702 (1.7V). That's probably more than any laptop except rare exceptions. At higher impedances it's still limited around 1.7-1.9V. Taking the least sensitive of the K701 and Q701 sample data on InnerFidelity and rounding down, that would be around 104 dB SPL maximum from the E7 with those headphones, pretty loud for a lot of recordings.
If you look at the sensitivity data for DT 990 250 ohms, assuming the Pro isn't quieter than the Premium, at a given voltage, the DT 990 250 ohms should be
quieter than the K702:
http://doctorhead.ru/images/misc/catalog/beyerdynamic/dt_990_pro/fr.png
http://doctorhead.ru/images/misc/catalog/akg/k702/fr.png
And the voltage an E7 can supply to the K702 exceeds what a typical laptop or an iPod could put into a DT 990 250 ohms (or any headphone).
So the K702 with E7 will be louder than DT 990 250 ohms with a laptop / iPod.