I have seen data sheets that give operational life as much as 300,000 hours (34 years), with a shelf life as high as 10 to 15 years "...without deterioration of quality". What will affect the life span is the ambient temperature (if too high, the caps will start leaking current), the ripple current frequency and the initial temperature rise (on/off operation). If you leave the amps off, then you increase the life span by virture of zero frequency but lose it when you turn on the amps (high initial temp rise). If you leave the amps on, then the reverse is true - so, to me, it's a wash whether you keep the amp on or off.
But 8 years to a ps filter cap? Doesn't sound right to me, nor have I heard that Krell caps have such a problem; however 34 plus years for a cap is, IMO, a bit on the optimistic side. I would guess that 15 to 20 yrs would be in the ballpark. Then again, my ML 20.6 pc boards were replaced twice in 15 years. Because of bad caps.
But 8 years to a ps filter cap? Doesn't sound right to me, nor have I heard that Krell caps have such a problem; however 34 plus years for a cap is, IMO, a bit on the optimistic side. I would guess that 15 to 20 yrs would be in the ballpark. Then again, my ML 20.6 pc boards were replaced twice in 15 years. Because of bad caps.