The only sure fire way is to plug in a analog TV tuner card (it does not have to be connected to anything you can do a manual setup) then run the TV setup. If you do this then VMC will use the downloaded TV guide instead of the OTA guide you would normally have with DVB-T card (as this is what VMC sees the DVB-C cards as).
Once you have done that you need to then go back into the settings screen and edit the channels. VMC will merge the channels that it can recognise but the others will need doing manually, the channels from the DVB-T card will generally start at channel 1000.
So for example you have BBC One on channel 1 (this from the analog guide) and channel 1070 (this from the DVB-T source) you edit channel 1070 then goto edit listing and select BBC One (channel 1) it then asks if you want to Shift, Merge or Cancel you select Merge then select the first option on the next screen (cannot remember the wording) and it will merge the 2 channels leaving only Channel 1 in the guide and removing channel 1070 now all your tuner sources will be mapped to channel 1 and you will have the correct guide data....
You have to do this for each channel that you need...
