Interesting response,
I have found just the opposite with my customers and Richard Gray.
First of all it depends on the Gray, we sell mostly the largest 1200's which usually make a terrific improvement.
But you might not be aware that you can plug a Richard Gray next to your amplifier on the same circuit and reap the same results, you don't get the MOV, for the amps, but the Gray in of itself will absorb big shocks to the system and still offer a degree of protection.
I never use the small units with big amplifiers, so if you tried a 400 or a 600 you may not have really heard the Grays.