the e11 is a pure amp. the e7 and e17 are dac/amps. if youre just lookin for an amp. the e11 would be fine. the PA2V2 would work too, also a pure amp.
im in a similar situation. i want an amp for my m50's. ive never used a dac before, so i also want to try that. not sure if its worth payin more for the e17 when the e7 is similar. let me know what you decide on.