I could not find the Bush site but from the little I could find, it appears that your B Pro 300 contains only amplifiers - no decoding circuits. So its as you say. You'll need something else to decode the signal. There are many DVD players that can do that. Look for one that has "multi-channel analog out" plugs. My Pioneer DV563 has them.
A DVD player cannot accept an input. So you're out of luck there.
Regarding the TV and PS3. you need something to decode the digital signal but TV's and PS3 do not have them. Does the Bush have inputs for other audio sources? If so, you can run the audio out from the TV and from the PS3 to the Bush and get stereo but not surround. The Bush may be able to "simulate" surround from a stereo source.
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If there are lawyers or politicians involved, logic may be a very poor tool for reaching a conclusion.