Samsung HT-D5100 upmixing Stereo to 5.1? (1 Viewer)

Hi all, I've seen many helpful threads here, but never posted anything until now, hopefully I have some luck, too
I have:
-WDTVLive device:
http://www.wdc.com/en/products/products.aspx?id=330
-Optical cable
-Samsung Blu-Ray player with integrated 5.1 surround, "Model Code : HT-D5100Series_ZC":
http://www.samsung.com/us/support/supportOwnersProduct.do?prd_mdl_name=HT-D5100
User manual here:
http://downloadcenter.samsung.com/content/UM/201202/20120202151939228/HT-D5100_XAA_web_1224.pdf

The D5100's Digital In supports only DTS and Dolby Digital audio, so I only chose those in the WDTVLive's output options.

When playing a DD5.1 file through the WDTVLive, through the optical cable, to the D5100's Digital In, it plays beautifully, I love it.

When playing an AAC2.0 file the same way, it plays through 2.0 speakers only. I would like all audio to play through all the speakers, even if it's only coded in Stereo (or even Mono). How can I do this? I couldn't find a function like that in the D5100's menus.
Edit: I got it to upmix using (in the D5100) Dolby Pro Logic II, but it only works in "Matrix" mode (not Music, Movie, or Prologic). Shouldn't it work in any mode? I thought that was the purpose of ProLogic?

IT is completely possible that the DPL only works(completely) from a disc.

I'm absolutely shocked DTS works on the optical input. Typically the only thing that you get using an optical with HTiB is DD, cause they are only intended to be used with a cable/sat box. OTA based audio only uses DD, so that is all they are, typically, designed to handle. So count your blessings it even plays AAC 2.0.