I notice a definite difference between the Mad Dog 3.2 unamped from my Note 2 vs the E17 feeding into the Mad Dog 3.2 vs the E17/E09K going into the Mad Dog 3.2.
I doubt any of these is optimal for the Mad Dog, but the sound improves to my ears. (though truth be told, even unamped, it sounds quite good - and that's how I'm listening as I write this)
If you have the money though, the E09K is a good upgrade - it also seems to fix the occasional problem of interference/static/etc that I sometimes hear from the E17 on its own when using it as a DAC/AMP.
Would definitely love to try these out with higher end amps - though it's hard to beat the E17 for portability and utility.