I need to have a 5v supply with around an amp of current draw max, and a 6v supply with around a 4amps current draw max. I was thinking: instead of having two switching regulator circuits, just having one 5amp 9v switching regulator circuit feeding into an Lm7805 and an lm338t (linear regulators) to generate my 5v, and 6v rails, respectively. My Vin is around 18v. Pololu makes some nice switching regs that fit my needs.
Are there any potential drawbacks to this arrangement? I heard it referred to as a switching pre regulator. When answering please bare in mind I'm a hobbiest.