According to page 18 of the manual the i-plate that appears when changing channel or pressing the i button should tell you if it's Dolby Digital or DD plus. Black Hole has done a guide which has a link to the manual here
I can see were the OP is coming from. My venerable AV amp sometime needs a nudge to tell it to check again what the audio format it is receiving from my Foxsat HDR particularly after an ad break on Channel 4HD either getting stuck in DPL or DD mode when it should be switching. It is easy to hear DPL being treated as DD as you get a very thin sound with nothing coming from the front centre speaker but conversely you don't really know and there is no info on the i-plate which tells you that it is outputting DD as DPL and so the amp needs a theoretical slap.
I have just done a test recording of a programme with 5.1 ch audio, and can confirm that there is no indication on the i-plate, or front panel, that the programme is 5.1 ch or stereo.
Also, as far as I'm aware, the Dolby Digital and Dolby Digital Plus icons have never, nor will ever be used, as the box does not receive Dolby Digital signals, it simply transcodes the received signal to output the Dolby signal that can be recognised by an AV amp, or suitable TV.
As Graham mentioned earlier, when connected to an AV amp, this should indicate the presence of a Dolby Digital 5.1 ch programme.
OK there was a plan B that I spotted on Page 16 but this still may not work based on Brians previous post but here goes...
Setting Audio Options
Audio options are available only when the programme supports multiple audio languages.
1. Press the AUDIO button. - Each time you press this button, the audio language changes or the Audio Description soundtrack will be selected.
2. Select the audio direction (if available) using the left/right arrows.
â€¢ The mute function remains set while you
â€¢ You cannot set the audio direction when the programme is broadcast in Dolby Digital.
So it might be possible to try and change the audio direction and it will let you if it's stereo but not if it's Dolby. However as I noted at the top this might not be relevant based on Brians findings - so I don't know if this workaround is specifically dependant on Dolby Digital or just whatever the Humax receives in order to convert it and output to 5.1. Thought I'd post it just in case it would work.
Ah but, it could be DD2.0 rather than DD5.1 and still reported as being in Dolby Digital as happens when I view ITV1 HD programmes on Freesat. It is my AV amp which processes DD2.0 as DPL. Last year the BBC were accidently flagging DD2.0 programmes as DD5.1 (Springwatch comes to mind) which sounded very odd as there was no centre channel.
I am at the point where I can see my AV telling me its applying Dolby Pro, in which case my assumption is the source is stereo (of some sort), ot its saying its a Dolby Digital source, so I'm as happy as I can be without having any definitive source info.
My Yamaha AV amp automatically gives me Dolby Digital 5.1 on nearly all the newest BBC programs and on newer feature films on Channel 4, but I have never seen a DD symbol on the i-plate. ITV HD is always in ProLogic, I've never really looked into this as I was just glad the HDR Fox T2 could transcode the proprietary AAC format that UK terrestrial FreeviewHD uses, I don't think many other boxes do.
A little off topic, but do any of you have any idea why the HDR Fox T2 plays a Dolby Digital 5.1 humax .ts file in Pro-logic when accessed from a NAS drive, but plays the same file in full 5.1 when accessed from a USB drive?
A DD symbol in the I-Plate (or front display icon) will only be displayed if the TV channel transmits Dolby Digital, This has never happened in the U.K. and probably never will. The Humax will not display these symbols when it transcodes the audio into DD