"Impedances
Mic in:
3.4 kilohms
Channel insert return:
5 kilohms
All other inputs:
20 kilohms or greater" -
http://www.mackie.com/products/802vlz3/pdf/802VLZ3_OM.pdf
"Nominal Output Level
PHONES/LINE OUT jack:
-14 dBu
Output Impedance
PHONES/LINE OUT jack:
22 ohms" -
http://lib.roland.co.jp/support/en/manuals/res/62121932/BR-80_e04_W.pdf
This is as wanted, a low impedance output -> high impedance input, since
the mixer and the BR-40 do work, it must be the cable.
Unlikely that the cable is to long, but many jacks tend not to fit to
many sockets. Even if it should be the correct cable and even if it's
not broken, it could be, that the jack must not go completely plugged
in. I experienced often that 1/4 jacks have different construction
forms, so that they don't fit to each other.