Why does the K4006 have room for 4 caps when only 2 are used and can i upgrade or add caps to make the voltage more solid under heavy load?
Yes, you can add two identical caps.
If the amp should be turned off before the preamp then is it ok to hook the transformers for the K4004B and K8084 to the same switch because the K4004B will likely power down after the K8084 because of the capacitors on the power supply?
Also im using a DPST switch so both live and neutral are switched at the same time is this ok?
Should be fine.