what ohms were your dt880's?
Also the dt770 anniversary or limited edition or what ever its called are easy to drive with good bass. I don't know about to many low impedance headphones though.
The RME doesn't have enough power. You can invest in an O2 amp though for 100 smacks.
Its really worth investing in an amp because usually the harder to drive headphones offer much more detail and space. I would get a simple small amp and go for some headphones that can offer you the things you are missing from both.
Edited by grizzlybeast - 10/30/13 at 12:27pm