Friend, I am not getting any absurd info. I went through the product page of Onkyo 5105.
Home Theater Systems : HT-S51005 | ONKYO Asia and Oceania Website
It says only Dolby Pro Logic II. [transforms any stereo source into a highly realistic and convincing five-channel surround sound listening experience].
And i went through product information in the same webpage(pdf) and i see there too only Dolby prologic II is mentioned.
I went through other products of Onkyo and which supports DD decoder they clearly mention that. Hence i concluded that DD decoder is not available in 5105 based on onkyo's website.
Thanks,
Prakash