Technical background: The PSP had two processors. The main processor which contained a CPU and the GPU (and which all games used) , and the
Media Engine, a secondary processor reserved for system use that contained a CPU along with the audio hardware and video decoder block.
For the PSP's PS1 emulator, the bulk of the emulation was done on the primary processor, however audio emulation was done on the Media Engine (I have never been quite sure if this is for resource reasons or because of the audio hardware).
Meanwhile the PS Vita's PSP emulator emulates a PSP-1000, but with one very large exception: it only emulates the primary processor. The Media Engine is not emulated. This isn't a problem for PSP games since they could never directly access it, but presents a problem for PSP system applications, kernel mode homebrew (e.g. SNES9X), and the PSX emulator. PSP system applications don't exist on the Vita, and of course homebrew was never Sony's concern, so Sony decided that PSX emulation issues were an an acceptable tradeoff for not having to emulate the Media Engine.
So how does PSX emulation work on the Vita? Sony is still running the main section of the PSX emulator inside the PSP emulator, replicating how it worked on the PSP. The difference is that rather than emulating the Media Engine for the PSP emulator and then emulating the PS1 sound in that, Sony created a PSX audio emulator in the Vita OS itself. As a result, PSX emulation requires interacting with both the PSP emulator (which we control) and the Vita OS (which we do not control). For legitimate PSX games this isn't a problem, but for copied games it is since we cannot talk to the Vita's PSX audio emulator.
With that in mind, the short answer is that you're not going to be playing copied PSX games on the Vita any time soon. With some work it should be possible to get the TN kernel to emulate the PSX as listed above by embedding the bits of the PSX emulator we do have access to, but I don't know if that's going to happen (long story). Plus even if that did happen, there still wouldn't be any sound. That would require writing a new sound emulator, and there's no guarantee that it would meaningfully work inside of the PSP emulator. Proper PSX emulation may very well require going the Sony route and having the Vita do part of the emulation, in which case PSX emulation will not be happening until the Vita has been completely cracked.
