5.1 audio tracks playing as 7.1?

[trevrox]

I recently just upgraded from 5.1 to 7.1 (with two ceiling speakers for Atmos being added within the next few days).

Anyway, when I played a Blu-ray with a DTS 5.1 audio track, it was outputting in all 7 speakers without me changing the setting. Not that I mind, because I planned on doing so anyway, but I was under the impression if it wasn't mixed in 7.1 I would need to use Pro Logic IIx or something of the sort in order to get it?

My Blu-ray player is set to output unprocessed sound and I didn't mess with any settings on my receiver, it says that it is playing a DTS-HD 5.1 track yet I'm clearly getting sound out of all my speakers. It was my understanding that unless I tell it to, I will be getting the native audio track without any upmixing. So really I'm just curious how this is happening