Yes, the factory 8dn belt is the one Hartman says is too hard. He isn't wrong about them being a hard belt, but I think it is best to stay with an 8dn due to the "floating" secondary. The softer belts don't seem to hold up well. There is an aftermarket part that will lock the secondary in one place so the side to side movement is gone. I've never tried it but if the clutches were aligned and the secondary locked in perfect alignment, then I bet a softer belt would hold up pretty good. You'd be amazed how little it takes to wear the heck out of a belt if the clutches aren't aligned if the belt is a pretty soft compound.
I personally love the life I get out of the 8dn belts and don't find my clutches really getting all that hot from slipping, nor do I see an excessive amount of belt dust being generated. Keeping the sheaves clean by scrubbing them with a green scotchbrite pad in circular motions keeps them gripping the belt pretty good.
The "floating" secondary is in theory supposedly so the secondary can align itself with the primary if they aren't set up quiteperfect, but I've read that it doesn't necessarily always align when a lot of throttle is applied and the sheaves clamp down hard on the belt...it can be out of alignment slightly from time to time. Due to the side to side float of the secondary, even if the clutches are perfectly aligned it can "lock" into place from time to time out of perfect alignment. This is my theory why the softer belts don't hold up well for so many that have tried one.