The split ground bus with a separate power amp and preamp ground bus is the current standard that DIY amp builders use. That's what I show in the 5E3 layout at the top of this webpage but most electrical engineers will tell you a single point grounding scheme should be the quietest. The original 5E3 used a brass plate under the input jacks and pots that acted as the whole amp's ground bus but corrosion between the steel chassis and brass plate can cause problems in the long term.