From the Wikipedia page about Sky digiboxes:
"The latest DRX595 has dropped the RF modulator outputs"
http://en.wikipedia.org/wiki/Digibox
I'm actually amazed that the inclusion of an RF modulator unit wasn't discontinued long ago. The modulator's only (official) use was to provide a signal to TV sets without a Scart socket. Since Scart sockets have been standard on new TVs for around a couple of decades now, there would seem to be no logical reason to retain the RF modulators.
Chris