OK - had another go with a clean install of MythBuntu 11.10.
Everything appears to go as expected and I get the correct info as above to 'lstpci -v' but the response to 'dmesg | grep DVB' is simply:
[ 6.960210] DVB: registering new adapter (SAA716x dvb adapter)
and I once again can find nothing in the Myth Back End set up for Capture Cards.
Any ideas? Am I missing something obvious here?