So I'm just getting everything sorted with my demodulator on my set up. I have everything plugged in, and working so I just want to make sure please I have it all done right with the player itself. To access these lovely AC3 soundtracks, do I want my player set to "Digital Stereo" when I'm flicking through he audio options on my CLD-D925? Thanks in advance.

For DolbyDigital (AC3), you need a RF demodulator.

AC3 is recorded in the right analog channel of the disc.

Digital Stereo is just that, stereo sound. Each LD has analog stereo sound, most made after 1988 or so have Digital Stereo sound. Some discs made after 1995 have Dolby Digital surround 5.1 (referred to as AC-3) which physically takes the place of the right analog. The AC-3 only comes out of the AC-3 jack on your 925. You don't need to switch anything on, its always coming out. Likewise the digital out on the player (TOSLINK) is always putting out the Digital Stereo tracks. The audio switching on the player only switches what comes out of the analog line level outputs (you can have either the analog or digital stereo come out of the line level, but not the Dolby Digital since you'd need 6 line outs for that).

In order to use the AC-3 you need either 1) a receiver from the period with an AC-3 RF input, or 2) an RF demodulator that changes the AC-3 RF to the now-standard Dolby Digital signal (optical or coax) that can be used by modern receivers or a stand alone Dolby Digital decoder like the Harmon Kardon 303 which takes AC-3 RF and converts it to six line level outputs (for which you'd need a receiver that has multi-channel inputs).

For DTS its much simpler, just run a TOSLINK cable from your player to the receiver.

Thanks very much indeed fellas. That makes sense.

I have the demodulator, a very lovely Yamaha APD-1 which looks lovely sat next to my Yamaha RXV-673 receiver.

Let the good times roll...

The Harman Kardon ADP-303 can be modified by placing an optical output... it's very easy.
Then it can be used with every multichannel amp that has an optical input

Make sure you also have the analouge connected on the Left-total / Right-total as some Laserdisc PAL NTSC have analouge audio and if using optical/coaxial analouge won't pass though to the AVR.

Also some audio commentary recorded on the NTSC Laserdisc analouge Left channel and when switching though the audio channels via the remote the AVR should detect when its on analouge so you can select analouge Left to listen to commentary on some Dolby AC-3 Laserdiscs.

Enjoy the delights of Dolby AC-3 Digital.

Can a receiver with DTS decode that or is it something your LD player has to do?

A receiver with dts decoder will be able to play dts LD's.
It will however not be able to do Dolby Digital from LD if it does not have a AC-3 RF input,
or if you do not have a demodulator.

For ac3 playback, the "Audio" options on the D925 make no difference. The player pushes the AC3 sound (if present on the disc) out the "AC3-RF Out" cable regardless of the Audio setting. It's up to your amp to decide whether to listen to the demodulator or another source. The D925 has a nice little indicator on the display that tells you whether an AC3 track is present on the disc. (More precisely, on that side of the disc.)

Those audio settings determine which audio tracks on the disc are sent out through the ordinary RCA stereo outputs. You may be able to use this to listen to the raw undemodulated AC3 track if you really want to by selecting Analogue/R and switching your amp to the RCA inputs (turn the amp right down first!). On the other hand there might well be an internal logic bar to doing this - I'm not sure.

I use all three audio connections between my D925 and my amp. AC3-rf for ac3, optical and RCA. The amp has a built in prority for selecting the signal source: AC3 first, then optical, then RCA. The only wrinkle is that on analogue sound PAL discs, it thinks there is a signal on the optical cable and what one actually gets is silence. Fortunately, one can manually switch the input signal however.