Great thing about the SM3 is...you don't NEED an amp for them to sound great. For instance, they sound awesome out of the J3 alone. Sure, my Arrow can do some fun stuff, like crossfeed and bass boost, but it's wholly unnecessary. All of these things people are describing are due to the sound of the amps, not what it's doing for the IEMs...if you want flat and neutral, well...for one, the SM3 is really neither, and for another...nothing is more flat and neutral in coloration than NO amp at all.
However, if what you're saying is you're having impedance matching issues with your laptop, and you need to fix that, then you'd want an amp that provides variable/adjustable impedance settings. But if you just want an amp to add to the chain or you want a better DAC w/USB, then one of the amp/DAC combos like the TTVJ Slim or Pico DAC/Amp would be a great fit.