Surprisingly few components in Media Center are multi-threaded enough to take advantage of the new 8-core Ryzens.
Even things like 6-channel SACDs are limited to 4 threads for decoding, and overall, single-core performance is going to make the biggest difference.
The main advantage that Ryzen has right now is that it supports ECC memory, while Intel's mainstream CPUs do not. Unless you're planning on building a system with ECC memory though, I'd recommend waiting for the new 8-series CPUs from Intel in a few weeks time.
The Core i5 and i7 are going to have 6 cores with Intel's stronger IPC/Single-Core performance, or you could drop down to an i3 to save some money since they will be quad-core. I wouldn't be surprised if the 6-core 8700K is faster than an 8-core Ryzen for most tasks.
For video playback with ROHQ, the GPU is what matters. And yes, Ryzen lacks an iGPU.
Intel is pushing back hard by increasing the core counts while keeping prices the same though.
I went from an i5-2500K to an R7-1700X and it's been a big improvement in performance for many tasks. But those which aren't very well multi-threaded have not always seen a significant increase in performance due to the modest IPC improvement and lower clockspeed for Ryzen. (my i5-2500K was at 4.5GHz for 6.5 years no problem) I think the biggest issue with my i5-2500K was the lack of hyperthreading more than anything else to be honest.
I don't
regret buying a Ryzen CPU, but I maybe wish I had held off another 6 months to see what Intel's response to it would be. Then again, with 50TB+ storage in this system, it seems irresponsible to build a system without ECC memory.
I'm thinking that by the time NVIDIA have new GPUs out, I may end up keeping this as a server/workstation (it
flies for things like video editing) and build an Intel system for gaming.