First, if I were you, I'd go for the M3 over the M4. You'll love the extra openness and bass authority that the M3 offers. If you're looking for comparisons, see my comprehensive reviews and comparisons on my audio blog, here
, here here
. (That should keep you busy for awhile...)
You'll see that I've owned both the M4 and M3, and what motivated me to upgrade from the former to the latter.
Additionally, I used to own a Nuprime IDA-16 and (after 300 hours of break-in as recommended by an online forum post) I sold it and moved on. If you're interested in why I made that decision and what I have settled on, feel free to send me a PM.
Hope that this is helpful to you!