GridIroN
100+ Head-Fier
I can check M8 with Cayin C5 (I should get it tomorrow or on Monday). I did however try M7 with E18 (as amp only) - it was a brief comparison (several songs). The purpose back then was to compare DACs (E18 vs HTC One M7) - and the difference between M7/E18 amp vs E18 dac/amp was practically nonexistent. There was no noise, no hiss - nothing to complain about. So I think double amping in case of M8 won't make a difference either. I think if one amp is transparent and both amps are capable of hiss-free sound and are not susceptible to cellphone electromagnetic interference, you can double amp.
I would appreciate that a lot. I'm currrently using my M8 with Westone 4R's and an E11, and there is definitely some hiss, but I think that's the E11 being an entry amp with a high noise floor.