David is right- you need to do something about mechanical isolation for the 'table.
If the preamp really was damaged by something to do with the ground, then both the preamp and amps need to go back to Halcro to get the problem fixed. There is no way the grounding of the amps should have any ability to do what they did, unless the amps are improperly grounded.
Now I can think of a way that that might happen- if the amps don't have a proper ground, and if the preamp has no ground, then the ground cable for the phono *might* be the only solid ground. If the system was driven to high power, there might have been some significant ground current exercised on account of the power generated by the amp. If the phono preamp was the only path for that (through the ground of the 'table), components in the phono section could have been damaged. Mind you, this is only conjecture as I have no idea how the Halcro stuff is set up; this is simply a possible scenario how such a thing could have happened.
If the preamp really was damaged by something to do with the ground, then both the preamp and amps need to go back to Halcro to get the problem fixed. There is no way the grounding of the amps should have any ability to do what they did, unless the amps are improperly grounded.
Now I can think of a way that that might happen- if the amps don't have a proper ground, and if the preamp has no ground, then the ground cable for the phono *might* be the only solid ground. If the system was driven to high power, there might have been some significant ground current exercised on account of the power generated by the amp. If the phono preamp was the only path for that (through the ground of the 'table), components in the phono section could have been damaged. Mind you, this is only conjecture as I have no idea how the Halcro stuff is set up; this is simply a possible scenario how such a thing could have happened.