I'd sit out the first generation socket 1151 motherboards.
The 6700k really isn't a speed improvement over the 4790k.
If you're wanting a DDR4 based machine, I'd go socket 2011-3.
The 5820k at 4.4GHz will be faster (and has two more cores) than the 6700k... and you get quad-channel RAM.
The 4790k locked at 4.4Ghz is more than adequate for all but the most extreme of DAW circumstances.
Great performance, low cost, and runs cool/quiet...