I think the Little Dot MK I+ (about $130) and the HRT Music Streamer ($150) would be a nice combo but this goes over your budget a little. You don't "need" a DAC but its highly recommended especially if your already investing in a headphone amp. Another thing you could look at is the NuForce Icon uDac 2 its probably pretty decent and has a built in DAC its priced around $130 on Amazon. I think it would adequately drive your Grados speaking as Grados are generally pretty easy to drive. With that said I think the Little Dot/Music Streamer combo would be better, its all up to your budget.
At any rate I hope you find what your looking for and happy listening!
