So if you ever change service, cancel service, take the filter off, etc. the cable company will be able to read the box and see that there's (for ex) 400 dollars worth of PPV purchases stored on it ...
If you can get the cable modem to lock off of one of the lines after the splitter, then both of them will work. Look to see if the splitter says how much loss is there is for each leg. Go with the one ...