Get rid of the jumpers and make some new heavy copper jumper with spades. Get LARGER speaker cable first. Copper is how everything was voiced back then.. Use heavy copper and short runs, see if that helps..
The LACK of bass in a room or tone control issues with a receiver are pretty straight forward. They have a treble and bass control does that help? How is the room set up.. Large reflective walls, ceiling and floors? ALL that, and speaker placement.
Lot of stuff could change how it sounds. GEAR is in place, LARGE enough cable, speaker, listening position. After that, ROOM treatment..
THEN gear... maybe.. Need a remote.. I do..:-)
Regards