Nobsound passive volume with rca in/out. I currently use it to control volume for powered speakers with the volume knob annoyingly on the back of the unit.

Nobsound High Precision Passive Preamp Volume Controller VOL Control HiFi Preamplifier ALPS (RCA&HiFi Version, Black) https://www.amazon.com/dp/B07GRLV7XG/ref=cm_sw_r_cp_api_glt_fabc_89VRF6FN6PBW43SG4G1H?_encoding=UTF8&psc=1

Mackie big knob - I use the passive rca version.

Mackie Big Knob Series, Passive 2x2 Studio Monitor Controller (BIG KNOB PASSIVE) https://www.amazon.com/dp/B01NCUZ32O/ref=cm_sw_r_cp_api_glt_fabc_CHK4P2R77BMKARSF02SH

Schiit SYS - another good option. Might have to order directly tho.

Schiit SYS Volume Control and 2-Input Switch https://www.amazon.com/dp/B00K6Q2A4C/ref=cm_sw_r_cp_api_glt_fabc_2JSBF0NBKACPS1PHXMSM?_encoding=UTF8&psc=1