Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
I'm fairly confident the HDMI cable you own is at least an HDMI 1.3a cable, but if its a cable from the mid 2000's it can be the reason you get no sound at all from the Skybox.
The issue might be the Audio output setting on the Sky HD box, but if that were set to Stereo instead of Surround, I would expect you to have at least stereo sound.
The HDMI cable has to be the correct version to deliver Surround to the TV set.
Then....the TV should automatically select stereo or surround output...even though the speakers are stereo, not surround sound based.
So...I think the first thing I need to ask is this....do you at least get plain old boring 2 channel stereo on the TV speakers, or are they dead as a doornail?
Second, I should warn you that TV stations and TV shows are still pretty much stereo audio. And I don't think that surround audio is going to catch on with TV shows as much. The surround audio setup is used more in Movies and especially on DVD movies. Even more, you'll find Surround used quite well with Animated movies because they can create a 3 dimensional sound stage with animation, and the real world with real action doesn't support a 3 dimensional sound reference as well.
We hear in 3 dimensions, but recording in 3 dimensions....it's more subtle and harder to control during production.
Anyways, I mention that just to let you know that TV shows may never have surround sound due to that complexity.
Since you stated --
When my Sky HD box is set to send Dolby Digital over the HDMI cable (which is absolutely what I want), the TVs play no sound at all through their speakers
it does make me wonder if the TV at least receives stereo sound when the Skybox is set to stereo instead of surround.
when the Sky box is set to send stereo over the HDMI, the TV plays it fine. Tried a few new cabled but no difference. The TV will not play dolby digital over its speakers.
Stereo plays fine out of the Skybox...but Surround is coded differently than stereo is.
The good news is this -- We know the TV and maybe the HDMI cable are good, and now we have isolated it to the Skybox.
I'm pretty sure your TV set is ok, but it really doesn't work with Dolby audio. That's meant for surround amps. Do you by chance have a Surround amp with HDMI inputs on it? Then the Skybox can deliver Surround to the amp.
On the TV set, I think you have a choice of stereo or Dolby audio, but I think that setting is for your Optical output or you also have the HDMI ARC (audio return channel) that lets you send surround/stereo OUT of the TV to an audio amp using the HDMI /ARC socket on the TV set.
Samsung's information isn't very well detailed, but the intent of the Dolby settings on the TV set is to allow the TV stations that have Dolby Transmitters and Dolby TV shows to allow that sound to be delivered to surround amps. It can't change a TV set's speakers from stereo to Dolby unless the rear panel provides additional speaker connections for the surround.
Look at the menu on your SkyHD box a second time. Besides the Stereo / Dolby setting, do you happen to see another AUDIO out setting that gives you a choice of PCM and maybe Bitstream?
TVs need PCM coding, but Amps I believe can handle both PCM and Bitstream coding. If you're set to Bitstream it is possible that's why you get stereo but no dolby sound. It should be set to PCM, because that's what TVs use.
The Sky settings for HDMI are normal and dolby digital. The cables are fine - if I use them to connect to an amp I get full dolby digital.
My question was how to get the TV to play dolby digital over HDMI through its own speskets ad the advertising states it can.
I really would want to see a copy of that advertisement you are looking at.
I've gone over the F5000 series of TV, and have found two critical pieces of information, regarding Surround. And the F5000 series is what we call an "entry level" TV set, and there is no Dolby Digital Surround mentioned in the TV menu. It seems to require a Soundbar or amp to process outgoing signals that can be Dolby though --
And there is Virtual surround
I would expect that on entry level TVs but the 7000 and 8000 series is usually where you find the Dolby Surround processing on TV sets.
You stated --
how to get the TV to play dolby digital over HDMI through its own speskets ad the advertising states it can
Can you copy and paste the Website that shows that advertising here in your response? I don't know if its a misprint, or if it's correct, but something is incorrect, Whether it's Samsung's information or some other source. I just need to read it.