I expected the MacPro line-out jack to provide sufficient audio gain to drive my powered speakers but that's not the case.

I connected older powered computer speakers to my MacPro and discovered that the volume level (audo gain) from the rear line-out 1/8" stereo speaker jack is too low while plugging into the front headphone jack works fine. We don't want to continue using the front headphone jack because any cable movement cases crackling and our yellow lab seems to touch that cable often.

Should I add a pre-amp to the line-out jack or try new computer speakers to see if it increases the audio level enough?