Which playback mode is good using low network?
That is not depended from playback mode. But I am recommend try find other version of channel with low bitrate. Also some channels have more one bitrate you can switch in ProgTV (Menu -> Streams)
Do you mean play a lower resolution Channel?if so i notice in my IPTV service with my hardware set up most times a channel plays a lot better without buffering in HD then in SD ? but i have an idea why; because there are many iptv users that don't have good INTERNET speed and high end hardware/software and therefore overloading server on that specific SD Channel,while HD channels are
relieved of overloaded on HD channel.