YES, I've been waiting for this thread for awhile because im kinda stuck to what DAC to pair with my Swans MKIII as well.
Currently I am using the Audio GD NFB-12 with Yaqin CD3 Tube Buffer.
I would look into the NFB-12, for 250 shipped, its a hell of a DAC, not to mention that it has a superior amp in it creating more flexibility in the future for headphones etc... The reason why i added the Tube buffer is because i thought the sound overall was still a bit thin for my taste (NFB-12 is DAC on the warm side already) I prefer a very lush and thick sound in my music. I didn't want to scrap the NFB-12 because for its price and quality, I really don't want to sell it. So by adding the tube buffer (around 120bucks) and putting on some nice tubes, BANG! I get exactly what i want, a very thick, spacious, SQ, leaning towards the high end HI-FI sound if you get what i mean.
I've used the HRT streamer II+ before, definitely a great dac, simple and clean. Too bad, i prefer Optical connections over USB (just my thing)