And if I'm not mistaken, C7 could mean anything I believe. I think Robin64 mentioned this way earlier in the thread, but I believe C7 just simply means that Canoe can't run it, which could mean lots and lots of different things. I believe there's just a lot of overlap between C7 and Preset IDs due to the game asking for something, but since whatever feature is turned off, Canoe goes all HAL 9000 and says, "I'm sorry Dave, I'm afraid I can't do that." and returns a C7. I believe so anyways.
C7 basically means that canoe tried to execute some of the games code and it returned an unexpected result/error. I know, a pretty generic answer. But I just felt I should chime in as "can't run it" is kind of wrong. I've done a LOT of testing, and boot time results come as mostly 4 things, full proper boot, C7, Black Screen (No Border), Black Screen (with Border). The 2 black screen results are more of the "can't run it" variety. C7's can happen in the middle of a game. For example, when developing the Star Ocean patch, id see certain pointers get set wrong and point outside of the scope of the memory addresses. When that pointer gets executed the game C7's.
And while I'm at it, I might as well mention that yea. DSP1 is an exception to the special chips needing a specific preset id. To understand why, you have to look at the development cycle of the original VC ROM releases. DSP1 was supported from the start. Meaning the earlier branch of canoes ancestors code was designed to emulate DSP1 from the ground up. SA1, SDD1 and Super FX all were added later. And each are supported differently. SA-1 requires a PID to execute code, SDD1 requires a PID to bypass SDD1 calls and instead requires the ROM to be hacked in a certain way, and Super FX seems to just require a previously unused header byte to be set to a non-zero value (generally 0x0C). In the broadest terms, a PID is just a tag to allow a game to be executed with whatever unique specific functions/hacks/combination of features the devs felt were needed to achieve optimal execution. It's canoe equivalent of ZSNES/SNES9X old game specific hacks.