The only output you'd get from the first receiver is just the cable feed - there is no modulator built in. This is why I stated that you would need a second viewing card for the other receiver to enable you to watch whichever channels you wanted independently of the first receiver.
There is likely to be some drop in signal levels but that would depend primarily the level coming in to the house on your cable feed, and then also on the length of the extension to the second receiver and also on the quality of the cable used and the quality of the terminations. There is no easy answer to that other than to 'suck it and see'.........