I run my tvheadend server and client on an Intel Atom + Nvidia ION machine, so hardware should not be the issue. When trying to set up my tvheadend server for IPTV channels in germany I ran into some issues as well. I fixed them by piping the stream through ffmpeg like this:
(you probably have to install the addon ffmpeg-tools first)
Codepipe:///storage/.kodi/addons/tools.ffmpeg-tools/bin/ffmpeg -loglevel fatal -re -i <STREAM_URL> -vcodec copy -acodec copy -metadata service_provider=Streams -metadata service_name=<CHANNEL_NAME> -mpegts_service_type advanced_codec_digital_sdtv -f mpegts pipe:1replace <STREAM_URL> with the livestream url of your channel and <CHANNEL_NAME> with the service name you used in tvheadend.
Where do you set this?
Does this solve the 100% cpu when running x265 movies?