We've covered just about everything you need to know about the PS3 Slim, but the sleuths over at Engadget HD (via a translated version of AV Watch) found a chart that indicates the PS3 Slim can bit stream both Dolby TrueHD and DTS-HD Master Audio. That change actually isn't that surprising, since the original limitation on the "old" PS3s was due to an older HDMI chipset; newer HDMI outputs have no problem bit streaming the high-resolution soundtrack formats.
We have a PS3 Slim review sample onhand, so it was easy to confirm the rumor. We had the PS3 Slim connected to the Sony STR-DN1000 receiver via HDMI, and we loaded up "Appaloosa," which as a Dolby TrueHD soundtrack. After making a few tweaks in the XMB, were able to make the STR-DN1000's display say "Dolby TrueHD"--confirmation that the Slim was sending the soundtrack in encoded bit stream format. Next, we loaded up "Master and Commander," which has a DTS-HD Master Audio soundtrack, and that worked as well.
Unfortunately, the practical benefit of this feature upgrade is minimal. The "fat" PS3 could transmit Dolby TrueHD and DTS-HD Master Audio in uncompressed linear PCM format, providing the exact same audio quality as the bit stream versions. There are some cases where an AV receiver may process linear PCM differently than bit stream, but its rare. On the other hand, it's at least nice to have the option, especially for those guys who just have to see the words "DTS-HD Master Audio" light up on their AV receiver.