Heh, yeah, pretty much anything will do what he wants - since he's using an electronic kit and just adding a drum track to pre-recorded mixes it's going to take very little processing power. And I know he's set himself on the 2 SSD thing, but
tbh I'd be tempted to drop an SSD in favour of 32GB of RAM. Getting all the samples & drum sounds into RAM is going to be a lot better than swapping them off a disk, although I suspect that even 16GB would be enough to load the samples for a virtual kit - each individual sample is going to be pretty small.
It's an interesting workflow/setup - Recording the rest of the band separately to the drums. Not entirely sure I approve, speaking as a musician
But it doesn't sound like it needs anything particularly special in terms of processing (since most of the processing will be handled in the audio interfaces and the virtual instruments, rather than the DAW). I used to run my recording rig off a 45W triple core Athlon with a USB interface and that handled multitrack overdubbing and playback without any issues.
Thinking about the comparitive performance leaks we've seen, the R7 1700 should have similar IPC to Haswell E, and has a higher boost clock, more cores, and a much lower TDP than the 5820k. The upshot of that is that it should performance at least as well if not better, whilst producing a lot less heat so being much easier to cool (equals a lot less noise). I think he should be easily persuadable to Ryzen on that basis