We've tested a lot of HDMI extenders over CAT and HDBase-T.
Following extenders (over CAT and HDBase-T) have been tested and are confirmed to work 100% fine with CSM-1 as they accept 22kHZ audio.
Digitus 55100
BlackBox VX-HDMI-TP-3D40M
Crestron HD-TX3 series
we recommend using the analog audio jack in this kind of situation
In some occasions video won't pass the over the extenders because either because the extender doesn't accept a DVI signal over HDMI
