I have a UN46C8000. I'm not sure what other features are different aside from plasma vs LED, but here goes:
1. I take it you are streaming using the TV or are using the media player. If you have a STB and never use OTA broadcast or streaming via the TV then you'd never have to worry about ARC. As it is, you want to use the ARC feature to send audio to the AVR. On the UN46C8000, HDMI 2 is the only HDMI input that has ARC. It's marked HDMI 2(ARC) on the back of the TV, so this should HDMI cable connection to the AVR.
For me, dealing with the CEC switching issue is one of managing the power-up order of components on the system. If I do STB then TV then AVR, I'm "usually" alright. If not, then the AVR will tend to switch to the OTA TV signal. My living room is small, so it's not a big deal or annoying hassle for me to switch sources as needed. I could see others getting seriously annoyed by it, and maybe a universal remote is in order.
2. The UN46C8000 does support DTS within mkv, of course this is true as long as you know that the mkv contains a core DTS audio stream. As far as I know the TV does not support DTS HD streams. Start the video, go to tools, audio options and switch to DTS. The difference in enabling DTS is huge compared to downsampled stereo which, for me, my AVR converts to multichannel via Dolby ProLogic.
By the way, my TV manual says that it supports LPCM. I've tried to bit-for-bit conversions of lossless audio streams, Dolby TrueHD and DTS MasterAudio, to LPCM, multichannel wave, raw PCM but never had much success getting the TV to playback. DTS is perhaps the best you can do, but it does work and it sounds great.
3. I use Samsung's own PC Share Manager. The software does no conversion. If the audio stream is not compatible for some reason, it's fairly quick and simple to convert the audio using eac3to and repack using mkvmerge. There's a guide for this here:http://www.avsforum.com/avs-vb/showt...1#post13961911