Same here! Had no fan active right from my start in 2010, the SIDs are holding up very nicely!
(Beware, though, If you have 6581, they run a bit hotter and might require better cooling than the 9V 8580s or 6582s).
You could always also install passive heatsinks and drill add a few holes in the case PT-10 bottom for improved airflow - from the MB6582 photo-tutorial:
thanks - I have 6882’s, plus both airholes and passive heatsinks, so I suspect I was overdoing it a bit! fan now unplugged.
I think the other issue may be that the resistors I used for the combined output socket are a bit too large - the individual outputs sound much stronger and have a better signal-to-noise ratio.