What you see is what you get with that one: two guitars tuned CGCFAD plugged into Vox Normal channels. Worth noting that in most Vox amps the Normal channel cuts way less lows than the more famous Top Boost channel, but Thom and Jonny almost exclusively use the Normal channel these days so that isn’t unique to this song or performance. The only real secret is the interplay of Thom and Jonny’s playing styles. And I think some bassists would take issue with describing that C as “super low” – it’s a minor sixth above the E-string on a bass guitar, and keyboards go even lower. But that also shows the importance of context in music: in a sparse arrangement, a note can feel much larger than it would in a band mix.
Jonny hits a note on the low string, detuned to C, during The Numbers.