i think this isnt a problem of vlc because vlc use the device (for instance /dev/dvb/adapter0) to communicate with your dvb device. but on my oppinion its not a good idea to have more than 2 dvb cards in your system. everything of datastream must be trough the pci bus and worked up with all components, esp. harddisk, cpu and so on. i think you can realize a good working system with 2 cards - this also works here very well.
Not sure I agree (or we might not be talking about the same thing). All I plan on doing is to tune to a different source for each card and output the whole TS as a multicast stream. Last time I did build such a setup on a dedicated server, I had 3 cards in it and it worked fine, if I exclude memory issues in the long run and had to restart the processes periodically.
As you referring to the same setup or were you considering specific processing (ie: record to file, transcode, etc..)?