To Float or not to Float...

Never lift grounds on power amplifiers. you don't want that to go live with the currents that can easily kill you. If however your house is correctly earthed the breaker should go before there is any damage done to the equipment or more importantly you. Unless as said above manufacturer has a ground lift capacity on the board " no "always leave grund in place. if you have a ground loop "buzzing" noise lift the earth on the pre amp as interconnects can more than likely handle that current going back to earth. But as said check connections are tight and that balanced connectors are wired the right way in phase etc. Pull the power amplifier as far away from the sensitive circuits in the preamplifier as some are oversensitive and away from central heating circuits , strip lighting. There are many noise sources that cause these issues. Often here is no need to jump to lifting mains earth on audio gear.

jea48 is the go to person when it comes to electrical wiring and safety.  Trust his advice. 

 I also have a pair of DeHavilland mono block amps with the same ground/float switches, and in the manual it states that leaving the switch in the "float" position may result in a "cleaner sound".  At any rate, a fully functioning grounded power cord has done the trick...

If the grounding scheme of the audio equipment is properly designed and executed there will be no need for a ground lift switch. The chassis will simply be properly grounded through the AC power cord's third prong and doing so will in no way affect the sound.

@jea48 has been correct in his assertions.

linndec

... if you have a ground loop "buzzing" noise lift the earth on the pre amp as interconnects can more than likely handle that current going back to earth.

This is bad advice and potentially unsafe. Interconnects aren’t designed to handle this current, and lifting the AC ground could energize component chassis with lethal voltages.

It amazes me how often people here misunderstand ground loop problems. The issue isn’t having multiple paths to ground; the problem is having multiple ground paths at varying potentials.

This is one of the benefits of using dedicated AC lines - it simply makes it easier to have clean grounds. I have a biamplified system with lord knows about many ground paths! I don’t have any hum issues, though, because of these clean, direct grounds ... all at the same voltage potential.

If your equipment has a ground-lift switch then it should be safe to use if you desire. Whether the connected components have the earth ground prong or not doesn't matter as long as they're properly designed. Simple as that. 

Unless you plan on opening your gear while it's connected to power (or immediately after a disconnect) then you have nothing to worry about. 

 A strong surge can destroy your gear regardless, so get redundant surge protection on your lines.