Can I use ECC33 valves on my CARY CAD 300sei amp?

As the title says, I am not sure if its possible, so, would appreciate any information please. I contacted to CARY Audio and got this info about plate voltage of 6SN7 inputs and however it looks good, there is one thing that makes me wonder and thats the plate voltage on 2nd input where pin number 5 stated at 580V. Does it mean that its simply to high voor ECC33, where 300V been stated as the highest possible.

Here is the details from CaryAudio:

The 6SN7 in the 300 SEI has the following voltages applied.

Input tube 6SN7
Pin 130V
Pin 3, 3V

2nd 6SN7
Plate pin 2 and pin 4, 278V
Plate pin 5, B+2 580V
Pin 6, 290V
Pin 3, 12v

I have used them all the time in my Cary 300 SEI with no problems. I was told along time ago by Kirk Owens who worked at Cary that it was OK. He's the one sold that sold them to me.
Many thanks for your replay, great. Are they really that good that they been described online, say comparing to CV1988 Brimars?
Already tried them, no probs, great tubes, thx again.