You can split a DirecTV coax, but it requires something called a multiswitch; you can't use a normal coax splitter and simply feed two receivers--it has something to do with odd/even transponders and a signal going back from the receiver box to the DirecTV dish.
I'm confused though--it you split one of the DirecTV lines, don't you still need another run of coax?
Theoretically, however, you should be able to use something to multiplex the CATV signal onto one of the coax runs, and then use something to split it off either in the LR or DR. Look at the boxes (SAT-D2?) on the following site (just a quick search on my part, may not be the best place to buy 'em):
http://www.hometech.com/video/dssmulti.html#MULTI
I'm confused though--it you split one of the DirecTV lines, don't you still need another run of coax?
Theoretically, however, you should be able to use something to multiplex the CATV signal onto one of the coax runs, and then use something to split it off either in the LR or DR. Look at the boxes (SAT-D2?) on the following site (just a quick search on my part, may not be the best place to buy 'em):
http://www.hometech.com/video/dssmulti.html#MULTI