I had a couple of 2089 models. One had two necks but I remember the only difference was the finish. No change in shape or taper, so they sounded the same. I tried one with a solid silver neck from a 989 I had, too. Same result.
Thank you for your feedback.
Some additional feedback I received, "As in all options of rose or red brass material for necks & bells on saxes, bells and leadpipes on brass instruments, the difference is felt more for the performer than heard from the audience.
That, "It is a subtle change in sound and only perceptible when you compare the different materials side by side."
And, "Also, on all wind instruments and particularly on woodwinds, mouthpiece/ligature/reeds combinations do more to change the sound than a rose brass neck."
I don't think I will fret too much about finding a red brass neck for my JTS-2089 XO, especially since they are also so hard to come by for this older model of saxophone.
Cheers.