I haven't tried the E10 myself but I highly doubt this would be the case. My 600s are too quiet plugged straight into a super weak android smartphone, but not by a lot. The E10 should power it to adequate volumes easily and the 250 ohm DT 880 should be the same. Though I wouldn't be surprised if he decided to upgrade his amp sometime down the road... I just don't think he should avoid the 250 ohm 880 and 600 based on inadequate power to push them as I'm willing to bet he'd be happy with the volume level of either phones pushed by the E10. Unless the E10 is no more powerful than a decent laptop audio jack, for example the ones in Thinkpads. But.. the E10 would be fairly worthless if that were the case. IMO.
Just because headphones play at a decent or even loud volume doesn't necessarily mean they are being adequately powered. For example the Ultrasone Pro 750 will sound plenty loud straight out an iPhone. However, it will also almost completely lose its bass.
Edited by KG Jag - 7/2/12 at 4:19pm