At one point I was having this theory-
Seems I was wrong. K1 did actually had a BGM implemented as ambient sound/SFX. We could hear it in the Upper City - North Apartment module [tar_m02ad] particularly with the Yun Genda/Sarna's quest. The relevant SFX is al_en_emptybar located in the 'streamsounds' folder. Though, the execution is not as smooth as TSL's Ent. Promenade which having that virtual surround feeling but still- it is something that can be explore.