005: It sounds to me like your Bluray player is sending out a stereo or Prologic downmix over analogue to your receiver. It also sounds like it is capable of sending out the core DTS track via S/PDIF, but your receiver has Dolby Digital only. Am I understanding what you mean correctly?
If that's the case, you'll probably need to upgrade your equipment to get 5.1 from most Bluray discs. If your current receiver has multichannel analogue input capability, then a player with this kind of output and the ability to decode all the new codecs would be your best bet. As long as the player's digital-to-analogue conversion is of good quality, you'll get HD audio regardless of how it is encoded on the disc. The other option is to get a new receiver, so that you'll at least be able to bitstream the core DTS 1509 tracks with coax or optical. (Of course, by upgrading both you could send all audio via HDMI, but that's down to how much you can afford.)
Of course, one must never discount the importance of good speakers. It is entirely possible to get better results from lossy codecs heard from high quality speakers than from a lossless signal played through a flimsy low fidelity system. It is for this reason that I highly recommend anyone looking for a new audio setup do themselves a favour and get some real speakers, and avoid HtiB's. Not only are HtiB speakers usually of low sound quality and high distortion, their small size means they cannot reproduce the audible spectrum its entirety--there will be 'holes' in the frequency response, particularly in the midrange, meaning that the sounds our ears are most sensitive to will sound thin and weak. This also forces the subwoofer to be crossed over at a higher frequency than is desirable, meaning it can be localised as a source of sound. If you can hear the bottom end of voices coming from the sub, something is seriously wrong! The subs themselves tend to be little more than noise makers, over-emphasising distorted tones around 60 hz to compensate for the fact that they can't actually get much deeper than that.
Avoid anything from Bose like the plague--contrary to their ubiquitous advertising campaign, they are not of good quality, and in fact exemplify all the bad traits I listed above. Even other HtiB's would be preferable. The fact that they claim to be hifi and charge at least six times what their products are worth is one of the great crimes of the audio world; that so many people believe them without question shows how little many know about what makes for good sound.
I don't mean to sound like some kind of audio snob or anything like that--I don't exactly have the world's best sound system myself, not even close. But with a bit of research and effort it is quite possible, even easy, to put together a system that greatly exceeds the quality of an HtiB, and for not that much more money either. Depending on budget you may have to build it over time and get only a few components at once, as I did, but it's well worth it in the end. When I was starting out I found the 'HtiB Alternatives Thread' on avsforum to be a very useful place to look for recommendations.