Many thanks for your help. After reading your post I got my multimeter out to test the jumper. That was fine but I discovered that the RPM pin was shorted to pin 1 on all of the connectors. I discovered that there was a blob of something conductive on the back of the splitty. When I cleaned this off with isopropanol everything started working again.

Further investigation - I've taken the machine apart to get to the back of the Aquaero. The pumps show correctly on aquabus when connected individually. They do not show when connected via the Splitty9, even if only one pump is connected. The splitty9 is connected to the Aquaero by a 4 pin aquabus cable. The pumps are connected to the splitty by 3 pin aquabus cables. The splitty jumper is set to Aquabus. Could it just be that my splitty is broken in some way?

I rebuilt my PC and am setting up Aquasuite again because I forgot to export my settings. I have two loops with two Aqua Computer D5 mps pumps. These are connected to the motherboard by USB. They are also connected to an Aquaero 6 XT by an aquabus cable via a Splitty (set to aquabus). The pumps show up as mps devices in Aquasuite when connected by USB. The pumps do not show up as Aquabus devices in Aquasuite. I have tried "find aquabus devices" and "reduce bus speed". Does anybody know why this ...