Up to now all 300cfx have the standard red Spirit installed, but I'm in the process of changing on one of them to a µSpirit without any trouble so far.
And yes, all three get the power out of the Hobbywing ESC for the Spirit FBL and the 4649T is powered through the RUDD port of the Spirit unit.
And as Tomas described, if you adjust more than 60Hz frequenzy to the Savöx servos, they cause even more trouble. On Blade 300cfx with the standard FBL system AR7200BX these servos cause also problems, if one puts more the 60Hz on them.
To connect the 4649T you use the Y-harness that comes with it.
The female plug of the Y is for the bind plug.
http://manual.spirit-system.com/index.php?title=Spektrum_IntegrationThe male plug goes to RUDD port, but remove the blue wire (Signal) first. The blue wire goes to the Aile-pin of the E/P/A port of the Spirit FBL. Since the rpm sensor of the Hobbywing ESC (plug with the yellow wire) goes to the PIT-pin of this port as signal for governor, you can install the blue wire into this plug and you are done.