Let me start by saying I love Plex and Kodi. Plex is great for remote access to your content and streaming to devices like your phone, the Roku, Chromecast, Amazon Fire TV, etc. Kodi is better for a dedicated media center PC. It can be a bit high maintenance depending on what you want to get out of it, but it's extremely customizable and easy to get all your content loaded up.
The big draw for Kodi is its support for HD audio (Dolby TrueHD, DTS-MA). If you're serious about a great home theater experience, you'll keep that audio track in the file you rip from your Blu-Ray. Plex will transcode the HD audio track for devices that can't understand it. But if you have a receiver that understands HD audio, then you don't want Plex getting in the way of that. If you want to pass HD audio to a receiver you will need the hardware and software that support it. Kodi is a great software option for this. It has an audio passthrough option that sends the audio straight to the receiver untouched. But what about hardware?
A couple years ago, I built a small cave to satiate my HD audio needs and the best device available for this was the Intel NUC. It cost around $350 for the i3 box, 30GB of storage, and 2GB of RAM. I thought it was a little pricey but it was the only viable hardware option available that could pass HD audio.
Well, a couple years go by and enter the nVidia shield. Originally released in 2013, it runs on Android and has some beefy hardware running underneath. It's an Android TV set top box which can run Plex and Kodi along with all the other apps the come with Android TV. In September of 2015, it received an update that enabled support for HD audio. Install Kodi on this and you're all set for HD audio passthrough to a receiver. Miraculously, it's also powerful enough to run a Plex server. Those of us with the space or desire to run Plex on a dedicated server will go ahead and do so. But, if you're looking to run a Plex server on something besides that desktop computer, then the nVidia Shield should be up for serious consideration. For $200, it can be a Plex server, set top box, and Kodi media center with HD audio support. And that is a real steal.