Thanks Peter, I hope you get a positive response from Adobe.
I did contact an Australian reseller yesterday, who was also very surprised but checked with Adobe who told him the same thing - no upgrade path from RH 9 to RH11.
Bizarrely, it seems there is an upgrade path from RH 9 to Technical Communication Suite 5. But cost is beyond my budget, apart from it including things I either already own or don't need.