Thanks Mogrim and scotroutes. I hadn’t thought about the brake problem with dual control, but having just done some quick searching it looks as if the two systems are incompatible (one is open and the other is closed), and I really can’t give up on the HS33s. The bike is a Roberts Roughstuff so I can’t fit disc brakes to it without major modifications, and while it’s currently a pain to change gears after a long days riding I can at least do so, whereas on my old v-brakes I was ending up finding it hard to stop when going downhill because of losing grip.
I’m going to get new cables and outers all round, and a new left hand trigger shifter (in place of my old SRAM Rocket) which it seems should be a Shimano R441 to go with my Shimano R453. I need the R453 front mech as it has the range to go with my Ultegra triple, and allows trimming – I’d forgotten about that until just now.
If I can buy T1000’s double taps I’ll give them a go as well. If none of that helps I’ll take a closer look at my Di2 options, but it’s crazy money so I’ll avoid that if I can 🙂