BSS DPR-402

"For vocals Stan puts Jeff Tweedy and John Stirratt through a dual channel Summit Audio tube compressor… usually. At the time of the taping, one channel was acting up and John’s vocal was put through a dbx compressor at the bottom of the rack. See, jujitsu. Acoustic guitars, piano, and keys are processed through BSS DPR-402 and 404 compressors; drums, bass, and effects are sent to dbx 1066 gate/comps," reads [this post](http://acltv.com/2012/09/14/gear-blog-wilco/) by ACL TV.

Optical lists it in this reddit AMA comment.

According to the "equipment list" found on Church Studios, owned by Epworth, one of the things listed is BSS DPR-402.