1) install v4l-dvb with new API, eg s2-liplianin ('http://mercurial.intuxication.org/hg/s2-liplianin/')
2) apply patch 't5882_S2Api_3.diff' in 'mythtv' directory (patch -p0 < [folder with patch]/t5882_S2Api_2.diff)
3) configure mythtv with option --dvb-path (eg './configure --dvb-path=/usr/local/src/s2/linux/include')
4) make, make install
5) add a new transponders with 8PSK modulation; modulation system and roll-off will be set automatically
when you scan

note: temporarily all DVB-S cards are considered as DVB-S2