Speaker is the load to your amp and speaker components tend to go old especially the voice coil, looses flexibility, expands so much that it's in friction with magnet just like joints that may catch later on arthritis. Depending on stress it may or may not contract or expand free.
Old speakers need re-work and re-work on old speakers with limited possibility to get correct crossover and driver parts may be very challenging. It can be done easier if you will use outboard electronic crossover but even that having in mind, you may end up finding better complete speaker for the project price. You've mentioned yourself that it'll be odd about all three source components and that's where you've found the answer to your own question. Now ask the same question about both of amps... The fact that you've fried already amp once is evident that speaker voice coil failed to contract/expand once and will do it again and probably more frequent sucking out your budget for replacement pair.
Furthermore I'd advise you not to connect to your rig any of your current speakers at this particular moment. You can get any low-priced floor-standing JBL, Polk or Klipsch from Best Buy and return it within a month to see if your components will expose the same intermittent problem.
Hope I found the best and diagnosed at my best your intermittent problem.
Old speakers need re-work and re-work on old speakers with limited possibility to get correct crossover and driver parts may be very challenging. It can be done easier if you will use outboard electronic crossover but even that having in mind, you may end up finding better complete speaker for the project price. You've mentioned yourself that it'll be odd about all three source components and that's where you've found the answer to your own question. Now ask the same question about both of amps... The fact that you've fried already amp once is evident that speaker voice coil failed to contract/expand once and will do it again and probably more frequent sucking out your budget for replacement pair.
Furthermore I'd advise you not to connect to your rig any of your current speakers at this particular moment. You can get any low-priced floor-standing JBL, Polk or Klipsch from Best Buy and return it within a month to see if your components will expose the same intermittent problem.
Hope I found the best and diagnosed at my best your intermittent problem.