Hi there and welcome to the forums,
You will need two HDMI leads for a start. Connect the Denon DVD players HDMI output to the IN1 HDMI on the Onkyo then the HDMI out of the Onkyo to the HDMI in on the Samsung. You may well need to refer to the manuals of the individual kit to set up the HDMI as sometimes they are not the default output / inputs. I know the Denon requires you to press the HDMI button on its front panel before it outputs thru it.
It may well be better to hook the DVD player to the TV via scart in the first instance to check if any adjustments are needed to initialise the use of HDMI.
OH and dont forget to hook the Denon to the Onkyo via a digital lead (optical or coax) for the sound and again, check to see if this needs initialising from the manuals.
Give it a go and give us another shout if you need more help.
You are quite correct, HDMI wont send the DD / DTS signal to the amp from an SD upscaling DVD player (like my Denon DVD1930), thats why you need a co-ax or optical digital lead. Having said that, neither an HD DVD or BLU RAY player can send the HD sound to the Onkyo (even though the will de-code the HD bitstream) there are no HD players capable of sending the raw data out of the HDMI socket as yet.
I did phone my local HI-FI shop (Acton gate audio in Wrexham) to find out how much it would be to part-ex my Denon AVR2805 against an Onkyo 605 as I wanted to get myself "futureproofed" ready for when the full initialisation of HDMI HD audio on the players. He said in all honesty, that the Denon would still more than hold its own against the Onkyo in the sound department (no offence to ANY Onkyo owners intended) and that even though the Onkyo has all the latest "bells n whistles" I would be better off keeping the Denon for a while longer as he stated what I said earlier about the lack of compatible players, and the only way (at present) is to use the 5.1 (7.1) phono outputs to get HD audio (which again, he reckoned the Denon does better than the Onkyo).
I found this to be refreshing that a HI-FI dealer was'nt willing to take my money and run, instead he gave me some sound advice and told me to save my money till things have settled down and then make a decision on what to upgrade to.
I would think you would get stereo information (any who wants to correct me if I'm wrong please feel free to do so) as in the first instance the Tosh will not output HD audio thru the HDMI (though it may send surround), plus even though the Yammy has HDMI connectivity, it does not de-code HD audio only the core DD / DTS surround information when connected via co-ax / optical digital audio inputs. The way to hear HD audio would be to connect the Panny to the Yammy via 5.1 analogue phonos (even then you miss out on the 7.1 HD audio that some HD discs contain.
Like I said earlier, I personally am going to wait a while longer till HD audio is available thru the HDMI connection method and then make a decision as to what HD /BLURAY player to get (have got a X-BOX 360 with HD DVD drive already as a taster to HD DVD), and what amp I will use to power it all.