The guitarron is played throughout NKIT, i'm pretty sure there's no other bass. In the How Long video Tim is playing an acoustic bass. I can clearly hear the guitarron when I listen to NKIT, but that could just be because I come from a mexican family and unfortunately grew up listening to mariachi music like Ronstadt did lol. I think they put a mic close to the sound hole like they did with the acoustics that weren't semi electric.