I think the 2600 just picked that moment to die. Most manufacturers have a pretty good idea how long their equipment lasts and adjust their warranty period accordingly.

Did you hookup of the 2600 and 1100 cause the 2600 to die prematurely? I doubt it. If the chassis were properly grounded then I'd think there's no problem running in this configuration. If not then I would have expected you to hear ground loop buzz well before now.

I also looked a little more into power conditioner operation ('cause I'm a nerd) and tying the chassis grounds together should not impact the surge protection.

Wouldn't hurt to get Monster's thoughts on the problem. They are the experts on their product.