If your TV only has ONE set of inputs, you can purchase a 20.00 Input selector switch. Basically, it allows you to connect up to 4 auxillary devices to ONE set of inputs, selectable using a push button switch. Just tune your TV to the input, and press the button you want to watch.
However, is you are splitting your signal before it comes into the cable box, I doubt you will need anything extra. One leg of the split goes to the TVs Coax cable connection just like it is suppose to, the second leg of the split goes into the cable box, out to the replaytv and OUT to the aux inputs on the Television. You watch analog TV just by changing channels, but if you want to watch digital channels OR recorded shows, you just switch to the TVs aux input and there you have it.