I've some questions about a good GND scheme
You will be less confused when you understand the reason for various connections, and the requirements that derive from that. The first step is to not use the term "GND" because it is ambiguous and will just lead to confused thinking.
First step is proper
protective earth (PE) connection for the power entry. That connection has one and only one function: protect you from electrocution in the event of power line connection to the chassis. As such there must be a short and direct connection between power entry protective earth and your chassis.
Solder is not permissible, because it can melt in a high current fault event and allow the connection to separate. Connections should be crimped or held with screws. Most jurisdictions require a toothed nut or other locking style connector which can "bite" into the metal and hold a firm connection without vibrating loose.
To reiterate, this connection is protecting you from electrocution, so not negotiable. There are very specific requirements for when a chassis can have no earth connection at all, involving insulation strength of the high voltage components and how many layers of insulation you have, but again that involves design which can result in potential electrocution hazard, so you need to know for sure what you are doing before attempting a non-earthed power design.
The next step is
shield connection of the cables. The shields of the cables are to provide protection from electrostatic fields, so to provide that function to as high a frequency as practical the shield connection of the connectors, i.e. pin 1 of XLR connectors, the sleeve of phone plug connectors, the shell of BNC, etc. should have as short and direct a connection to the chassis as possible.
A secondary result of connecting the shields directly to the chassis is that chassis-to-chassis leakage currents now flow on the shields. Any connection has resistance, which results in any current flow through that connection generating a voltage. That voltage will primarily be related to power line noise, so you need to make sure that there is no path for that noise through the circuit
reference node. Inappropriate connection that allows the shield currents to flow on the circuit reference is referred to as the "pin 1 problem" from a June 1995 Journal of the Audio Engineering Society paper which popularized that term.
So the terms I have highlighted, "protective earth," "shield connection," and "reference node" all have very specific functions, but people will commonly refer to any or all of those as "ground." Without keeping the relevant functions separated in your mind as you plan a design, you can end up with only tangentially related items connected together in ways that limit the audio performance.
Bill Whitlock (MisterCMRR in these forums) has provided access to a very good tutorial on this subject. It is well worth the time to read through:
Whitlock grounding and shielding seminar
[Edit for posterity: I found some clarification on the "solder is not permitted" claim I made earlier in this post, which is not strictly correct without caveats. What you should not do is rely on solder alone to connect a wire to a chassis, there should be a bolt and wire terminal, rivet, etc. that physically secures the earth wire to the chassis, and if the wire connection to the power inlet or terminal is soldered, the wire should be hooked or wrapped through the terminal lead before soldering so that if the solder does begin to melt the wire cannot fall away.]
