Dbarger,
As long as you have adequate power with the Ref 8s and you're happy with the bass extension, there is probably no reason to upgrade to the Ref 9s. The pair of Ref 8s I have are the 8.02, I believe, and I like them very much. My feeling is that the latest Reference 9s are a little better in the ways that I mentioned above. That said, the 8.02's that I have do not contain all the most recent upgrades of my Ref 9s. So it is very possible and likely that the most recent version of the Ref 8 does compete well with the Ref 9, in the midrange and treble (provided that NuForce is upgrading the latest Ref 8 in the same ways).
In my view, bass freaks and those with relatively inefficient speakers (under about 88dB/watt) may be better served by the Ref 9s (this is also dependent on the size of one's room and how loud one likes his music). Since NuForce has extended the bandwidth of the Ref 9s into the treble spectrum, to my ears they sound as fast and detailed as any pair of Ref 8s that I've heard. I believe the bandwidth specs that NuForce currently lists is outdated.
Realize too, that the power supply of the Ref 8s is limited by the smaller size of its chassis, i.e., it's likely that a higher capacity power supply wouldn't physically fit inside the compact dimensions of the Ref 8.
So right now, the relevant performance-related questions are completely dependent upon the specific version of each amplifier you happen to be comparing and which options (if any) they contain.
As long as you have adequate power with the Ref 8s and you're happy with the bass extension, there is probably no reason to upgrade to the Ref 9s. The pair of Ref 8s I have are the 8.02, I believe, and I like them very much. My feeling is that the latest Reference 9s are a little better in the ways that I mentioned above. That said, the 8.02's that I have do not contain all the most recent upgrades of my Ref 9s. So it is very possible and likely that the most recent version of the Ref 8 does compete well with the Ref 9, in the midrange and treble (provided that NuForce is upgrading the latest Ref 8 in the same ways).
In my view, bass freaks and those with relatively inefficient speakers (under about 88dB/watt) may be better served by the Ref 9s (this is also dependent on the size of one's room and how loud one likes his music). Since NuForce has extended the bandwidth of the Ref 9s into the treble spectrum, to my ears they sound as fast and detailed as any pair of Ref 8s that I've heard. I believe the bandwidth specs that NuForce currently lists is outdated.
Realize too, that the power supply of the Ref 8s is limited by the smaller size of its chassis, i.e., it's likely that a higher capacity power supply wouldn't physically fit inside the compact dimensions of the Ref 8.
So right now, the relevant performance-related questions are completely dependent upon the specific version of each amplifier you happen to be comparing and which options (if any) they contain.