One that requires constant focus (at least for CHIM, we don't know the specifics of Amaranth). But, if I understand correctly, there are other paths to Amaranth.
At least some paths that attempted to reach it. The Loveletter mentions Numidium, CHIM, the Psijiic Endeavour, the Prolix Tower (No idea what that is), the Enantiomorph and the Scarab That Becomes The New Man (No idea what that is too), and Vivec's sermons mention 6 ways to Reach Heaven by Violence, presumably the ones mentioned in the loveletter.
Also Vivec doesn't use CHIM because the whole nature of CHIM puts you in the state of mind where you don't want to use it. The only time he actually used it was to gain revenge on Azura and dissappear mysteriously.