Well, I can certainly see some merit with your method.
However, source first/amps last sequencing is the way it’s always been done in larger pro audio systems. IIR, the idea is to give the front-end electronics a chance to stabilize so that you don’t get a big “pop” in the speakers. The BFD equalizer commonly used for subwoofers is notorious for causing a pop in the speakers when it’s turned on, and with a sequenced start-up you won’t get any pop from it.
Turning off the amp first minimizes speaker pop by letting the amplifier capacitors discharge before turning off the front end components.
The vintage Adcom ACE-515 is one sequencer that does it right: At start-up it delays the amps something like 5-10 seconds, and on shut-down switches off the amps first, then waits 30 seconds before shutting off the source components.
Regards,
Wayne A. Pflughaupt