The new version of sage does not play nicely with SBS 2011 - when you run the installer for the data service it eventually gets to a point where it says your operating system isn't support (seriously Sage, what the hell?)
To get around this you have to install all of the components and prerequisites manually. Luckily, when you attempt to install the data service Sage leaves all of the installation files lying around in your user temp folder (%temp% at the run prompt and go to "Sage Accounts")
Once in there, you can go into the redist folder and ensure all are installed - if you run into error 0x80240017 whilst installing the dot net framework 4.6 (NDP46-KB3045557-x86-x64-AllOS-ENU.exe) then you most likely need to install SP1 on your server (
see here)
Once done, you can then go into the packages folder in the same location and run Sage50Accounts_DataAccess.msi (you don't need the ODBC one for just the data service).
If that installs - congrats!
However, If like me you receive more error messages about certain dll files not being registered (sg50SdoEngine240.dll in my case) and the services not starting, I had to re-run vc_redist.2015.x86.exe and perform a repair (this seemed to install with SP1, but the system really didn't like it) - this then let the software finally install.
Sage really need to sort stuff like this out, if they cant get the basics down then good luck to the people using the actual software.