Have you tried a Grundfos, I used to work for a plumbers merchants until recently.
The Grundfos watermill pump would provide 4.5-5 bar pressure compared to the 3.6 from the ESP...
If that is too strong they would do something a bit lower.... just make sure your shower heads can take it, if the pressure is too high they can pretty much just fly off the wall.
Grundfos are pretty decent, if you take the cover off the majority of boilers and look at the pump inside, you will find more often than not it will be a Grundfos so they are well thought off..... Never did get the fascination with Salamander, I think its just the kickbacks they offer merchants for stocking their products.