Upgrading to a better radio is not hard all, and mounting receivers is as simple as a piece of servo tape. The Flysky GT3B is a great radio for $45. And it can control up to 10 different RC's simply by buying a new receiver for each RC for around $10. How much is the Spectrum radio? I am betting...
Radios come with receivers that work with them. You can't connect any radio to any receiver. You have to find a receiver to match the radio you have, or buy a radio with a new receiver. Like the Flysky GT3. It will work with various Flysky receivers, but not all Flysky receivers