80dB should not be challenging at all, and should not be harmful to practically any HiFi floor standing speaker in the world. It is also doubtful that both speakers have failed in precisely the same way at the same time. Far more likely we are looking at an electronics issue.
I suspect your problem lies in the battery unit. I wonder if the charge from the battery supply is failing/weak, and thus would cause distortion when playing. I presume it would not simply fail like a light switch, but would falter and cause the distortion. If you have a software package for digital streaming that allows volume control through the software, then you could hook it up using the software volume control, bypassing the battery preamp and going direct to the mono amps. BUT, you MUST have software attenuation! Do NOT hook up the amps directly without some attenuation/level adjustment. With a more direct setup you can determine whether the preamp/battery supply is the culprit.
Or, you can buy an inexpensive attenuator and put it in line. You may actually prefer the sound of one of these alternative setups to the preamp in the system. You cannot know unless they are tried. So, you could turn it into an exploratory time for the system, too. Why not try to push for a big improvement while hassling with it? I use problems to spur me to move the rig to a much better sound quality. :)
Have you had power outages that could cause the battery supply to fail to charge properly?
If you still have problems, even after removal of the preamp, then you likely can zero in on the amps as the culprit. But, again, not very likel that both would fail identically. Perhaps you should isolate your speakers L/R and see if only one is acting up, or both. That would tell you something, too.
Recheck your connections.
I suspect your problem lies in the battery unit. I wonder if the charge from the battery supply is failing/weak, and thus would cause distortion when playing. I presume it would not simply fail like a light switch, but would falter and cause the distortion. If you have a software package for digital streaming that allows volume control through the software, then you could hook it up using the software volume control, bypassing the battery preamp and going direct to the mono amps. BUT, you MUST have software attenuation! Do NOT hook up the amps directly without some attenuation/level adjustment. With a more direct setup you can determine whether the preamp/battery supply is the culprit.
Or, you can buy an inexpensive attenuator and put it in line. You may actually prefer the sound of one of these alternative setups to the preamp in the system. You cannot know unless they are tried. So, you could turn it into an exploratory time for the system, too. Why not try to push for a big improvement while hassling with it? I use problems to spur me to move the rig to a much better sound quality. :)
Have you had power outages that could cause the battery supply to fail to charge properly?
If you still have problems, even after removal of the preamp, then you likely can zero in on the amps as the culprit. But, again, not very likel that both would fail identically. Perhaps you should isolate your speakers L/R and see if only one is acting up, or both. That would tell you something, too.
Recheck your connections.