Just as an aside, the PS3's capabilities with regards to bitstream audio output are only for the legacy codecs of DD and DTS. There is some speculation that a firmware update could resolve this issue, but I believe the general consensus is that the HDMI board itself, though "version 1.3" in spirit, was just a little bit too far out on the front end of this technology and lacks the ability to send Dolby True HD or DTS-HD Master Audio in uncompressed form. Of course, it also lacks the ability to decode DTS-HD Master Audio on board and deliver it via LPCM, so therein lies the fundamental flaw in the PS3's provisions for future upgrades.
At any rate, if you have a device that is capable of sending the new lossless encoded audio signals via bitstream (the field is pretty thin... I know I'll forget a few, but this includes the newer Panasonic Blu-ray players BD30 and BD50, I believe, the new Denon players, DVD-2500BTCI and the DVD-3800BDCI, supposedly the Samsung BD-UP5000, though at last check it was awaiting a firmware update to get this functionality working, and of course those that I've missed), you can set your player to bitstream and, assuming your receiver has the appropriate codecs, the "light" indicating the particular codec will illuminate.
If you send unpacked audio, whether it be a straight LPCM track, decoded DTS-HD Master Audio, or decoded Dolby True HD, you will only see the "PCM" light since at this point, the audio has already been uncompressed.
For those who may not be entirely sure, DTS-HD Master Audio and Dolby True HD have little, if anything, to do with the actual audio track. Either of these formats will present you with lossless sound, as will the LPCM track found on many Blu-ray titles. The difference between these formats is, primarily, not what you will eventually hear, unless Dolby and DTS are in some way involved in the way the tracks are mixed down and equalized (though the intent of these formats was to leave the audio untouched as it would be heard on the master tape). The difference is that LPCM is uncompressed, meaning it will occupy a good 4GB to 5GB of space on a given disc. Both Dolby True HD and DTS-HD Master Audio are effective compression schemes and can pack an LPCM track down to about 1.5GB or less. The sound from any of these formats should be close to identical (perceived differences are almost always a matter of baseline volume levels, with some people claiming that one sounds better than another, when in reality it is just a matter of turning the volume up or down a few dB).
In days of yore, Dolby Digital and DTS tracks differed in that DTS was a higher bit-rate format, but since both required compression that went well beyond just "packing" a lossless track, decisions about the application of the formats could result in very different outcomes. There have been many times that I found a Dolby Digital track more pleasing than a DTS track in spite of the DTS bitrate advantage. Those distinctions should essentially be a moot point at this stage in the technology. I believe the primary factor determining which lossless compression scheme a title will use is the arrangement the studio or distributor has with either Dolby or DTS. I'm sure there is cost competition involved as well, but the good news for us is that, really, either one will provide an exceptional listening experience. I'm mystified as to how DTS fell behind the curve in having its codec implemented more thoroughly in playback hardware.
I'm also somewhat amused that the "high def disc war" incites such fervent animosity between adopters, while those who would, for instance, come to blows defending Blu-ray as the superior format, decrying the existence of another disc because, "why should I have to pay for two players?!" are the same people who are anxiously looking to purchase a brand new x-generation Blu-ray player so they can get ahold of DTS-HD Master Audio. Shouldn't they be asking, "why are there two lossless audio codecs!?" Oh well, it's a funny hobby.