You're kidding, right? Sony have been very vocal about the incredible power of their hardware for over a decade. They gave us pretty clear descriptions of their hardware in PS4, but more importantly they have communciated with the developers using the hardware as to what's in it, and they didn't mention a DSP.
Now it could be the TrueAudio aspect is what's doing the mixing and decoding, in which case Sony have mentioned it as the functions it enables. In this case, the mention of TrueAudio would be what's throwing us, as we are associating that tech with a powerful hardware audio engine as described by AMD for PC. If the TrueAudio in PS4 is that same PC hardware though, that's a significant improvement in one area of PS4 and one Sony didn't mention, despite being clear about everything else in the system (two display planes, upscaler, 18 DX11+ CUs, 8 ACEs and 64 threads, 8 core Jag, HSA, Onion and Onion+ interfaces, ~2-GBs CPU to RAM BW, 8 GBs GDDR5, 172 GB/s BW or whatever it is, low-power ARM based background processor, video encoder/decoder...how much more info do you want if that doesn't count as 'in depth explanation of their hardware'?).
The nature of the hardware is significant in understanding PS4, and everything to date has been transparent. We've received an excellent understanding of the hardware. This DSP news goes completely against that, as simple mixing and decoding of audio could be accomplished by less than a programmable DSP.