And an AMD CPU with Radeon graphics. Little more oomph than a Pi3, presumably access to more X86 software and access to the fruits of the labor of the mature dev community around full OpenGL, instead of OpenGL ES2 on the Pi.
RetroPie's fun, and a great piece of software. Something faster than a Pi3 would open up more systems for reliable emulation, and access to x86 software simplifies a lot of things.
Maybe a bit off topic but, how is Kodi on a Pi at decoding high quality MKVs with DTS sound? I have a Retro Pi on a Raspberry Pi 3b, but haven't bothered putting Kodi on it as I have a Zotac Z-Box right next to it with optical outputs and all that jazz. Might be nice to consolidate.
Not sure about DTS (I think passthrough works, at least, if you have a receiver, and I'm pretty sure it'll at least give you stereo from it if you don't) but an RPi2 will do h.264 1080p video no problem. Any Pi, however, will fail to play the newer h.265/hevc codec at anything above maybe SD resolutions, as they lack hardware support for that codec and don't have anywhere near the horsepower to give you anything but an audio-desynced slideshow in software.
Depends on the video codec that the MKV contains. H.264 is handled with hardware decoding. H.265 apparently works in some limited cases, but I wouldn't count on it. VC-1 (WMV9) is supported for hardware decoding, after purchase of a separate license.
The audio is all software-decoded, but I think it can be configured for passthrough directly to HDMI, for at least some formats.
You are not required to have the Pi in a case. It's nice to do though. Fake USB SNES conrollers that work great on RetroPie are about $3 each if you search around.
