Balancing Speaker Volume

[fishercom]

I have a pair of Boston Accoustic wall speakers, 8 ohm, controlled by a volume control in the wall and powered by an old Onkyo TX2000 170 watt receiver. I recently added two outdoor speakers off of the same volume control and speaker cable because I could mount them outside directly opposite the indoor BA speakers without exposing any wires.....however the volume out of the outdoor speakers is much lower than the directly adjacent indoor BA wall speakers. In order to get the outdoor speakers loud enough I have to turn up the volume so that the indoor speakers are too loud. The outdoor speakers are also 8 ohm and rated at 80 watts each. I want to balance the two pairs of speakers.

Because the wires are buried in the walls and not otherwise accessible and I do not want any unsightly wires or equipment to show, I have to use the same pair of speaker cable in place for the BA wall speakers to wire the adjacent outdoor speakers. I do not have the luxury of running a separate pair of speaker wires from the receiver to the outdoor speakers with a separate volume control in the wall.

Could I add an additional type of "volume control" or variable potentiometer in line to the BA speaker hidden in wall speaker enclosure to reduce the volume level on this one to match the volume level of the outdoor speaker so that when I increase the volume on the wall control both pairs of speakers increase to the same loudness?

.....or is there another way to equalize the volumes on the two pairs of speakers easily and without unsightly wires etc.?

Chrys Fisher
FISHERCOM@AOL.com