They are incredibly talented, but in the few videos I've watched, I haven't seen them include an acoustic bass in any of their arrangements. It seems like it would add a desirable layer to their music. This is an impressive performance, but just lacks a little punch from a strong bass line:

https://www.youtube.com/watch?si=x8GSUZM0xcHoA57n&v=dfkDcaGatIY&feature=youtu.be