How can I get my new receiver to decode the AC-3 s

many of the newer model pioneer elite receivers still have built-in rf demodulators. i use the vsx-37tx in my HT system, and i know for sure it has one, since i use it for DD 5.1 from my LD. . .

check the features on the website, it'll say: ac-3 rf demodulator or something similar. or you can purchase an external one, as the others suggested.

sdcampbell, just fyi: you are incorrect in stating that ld's do not use dolby digital or other digital formats - it depends solely on the disc. many older ld's have an uncompressed pcm track as well as an analog-only track. and many newer ones *do* have DD and DTS tracks, along with a pcm and an analog track. they (the DD and DTS tracks) are indeed RF modulated and need to be demodulated in order for a receiver to recognize the signal, but that is because the commonly accepted technology changed for sending compressed digital data from rf modulated to using a digital cable with the popularization of dvd.
the standard analog tracks are not rf modulated, because they don't need to be. the go out via rca jacks like anything else. the pcm tracks as well would be decoded by the player's internal DAC and then sent out the rca's.