You have installed the tuner correctly.
This sounds like an image problem. We have integrated the S2 Tuners years ago and there are no such problems.
When the picture blocks you need to check whether it's a signal problem or the box is overloaded (or USB ports are overloaded - eg. if you use a USB Harddisk at the same time), the BER should give you some indication about that.
In openelec there's a sundtek plugin available, currently you can use it with tvheadend.
There is a network mode integrated in the driver, I'm not sure if you can enable this via the sundtek openelec plugin (the command line way to set up the network streaming is to run mediaclient --enablenetwork=on on openelec, with other systems it would be /opt/bin/mediaclient --enablenetwork=on)
For the near future we plan to release our own streaming server.
->
http://support.sundtek.com/index.php/topic,2075.msg16403.html#newFor sure there are no sensitivity issues with those tuners they have been tested intensively (we have tested them with around 30 different LNBs by now and every single tuner is tested before shipping them out).