The only way to install API v3.07. Is to install SDRUNO 1.4 beta. This will stop API V3.06 from running.
I have just tried a RSP1a, and it works fine in multipsk with all the files in SDRplay_RSP_TCP_1.1_API3.07_Windows.zip installed in the Multipsk folder.
After installing SDRUNO V 1.4 beta which then installs API V3.07.
The next release of SDRCONSOLE V3 will support API V3.07.
At the moment we are at a crossover point