I think that what Steinberg writes could be literally true, but it could also be somewhat poorly stated. Without seeing the data or talking to the people doing the testing it’s hard to tell (I’m referring to the “synchronization” sentence now).
The thing to consider I think is that the 6900k is on the x99 platform. It’s a proven platform but you should remember that Intel probably won’t produce any more CPUs for it. The newer x299 platform is out, and it’s probably too new to invest in ‘safely’ right now.
I would recommend sitting down at your current computer and opening up a bunch of projects and literally write down what type of work you’re doing, and how high the workload is. How many tracks are playing back, how many plugins are you using, how many VSTi, how processor-intensive are they? How many tracks are you recording? Are you recording with all of the other stuff running at the same time and with low latency?
Then you can look at the test data and get an idea of what a good solution is. I for example do pretty much only editing and mixing for post production in Nuendo, and my buffer size is probably 512 samples (I can’t remember right now). So for my type of work an AMD Ryzen 1700 would probably give me the best value right now. It’s cheap, it’s by now proven as a CPU, it outperforms a lot of the more expensive Intel chips, and it performs really well on the type of workloads I do.