the e11 is actually more powerful than the e17. The e17 has a built in dac and acts like an external "sound card" when plugged into a computer. If u dont neednthat function, stay with what u got. If u r using an iphone or idevice, just get yourself a line out cable (fiio L3 or L9). Since you already have the amp for portable use. You should just get the e10 for desktop computer use if that is within your needs. It will only be a 50 dollar upgrade and you will have the best of both worlds. Instead of droping over $100.
I purchased the L9 when I purchased my Q40s/E11. Thanks a lot man, this was really helpful!