You have to understand Nuforce policy for product support, which I think is better than most manufacturers.
Your Ref 8.5V2 can be upgraded to future V3, to Ref 9V2, Ref 9V2SE so there is no concern there. We decided not to sell Ref 8.5V2 (but if anyone want one, you can still order it) since it is too close to Stereo 8.5V2.
P-8S is essentially the same as P-8 except we reworked the preamp circuit for some improvement and the spec doesn't change. If you're happy with P-8, there is no point paying $500 extra to upgrade to P-8S.
P-8S is now $1650. We didn't raise the price of P-8 for 3 years and cost have been increasing.