The first thing to realize is that it is a whole guitar amplification system.
It consists of several components, and this compartmentalization is what makes this doable, regardless of the size of the circuit.
So let's run down the signal chain.
Starting from the guitar and cable, we arrive in the first major building block, which is the pedalboard unit.
This consists of several analog fx pedals, a BOSS GT-8 multi-effects unit, a DI and ReAmping interface, and the digital circuitry involved in making the connections between those parts.
From there on, by means of a balanced feed of several meter length, we move into the actual amplifier. this one consists of two booster stages, level adaption circuitry, another DI-Interface, four preamp channels with flexible tone stacks, two effects loops, two output EQs, and several types of power amplifiers, so output power can be selected due to the prevalent environment.
And, of course, there is some digital control means implemented here as well, interconnected by MIDI with the pedalboard, or controlled by any other MIDI controller for that matter. So, in essence, there will be two cables running between the pedalboard and the amp head, and that's it.
That's the system I have in mind, and right now I'm feverishly drawing up circuit diagrams to design the components of this system.
My personal goal is to make all this fit onto a single 155 square inch circuit board to order from goldphoenix, which I would seperate into individual modules manually,
and build any missing stuff on perfboard.
The midibox NG seems like the right start to base the pedalboard switching system on, and the money is still out on the (somewhat simpler) amplifier switching system.
If I manage to obtain a crossbar switch IC, I will use that as a rather elegant switching solution.
The power amps I have in mind and that I'd like to implement are LM386, TDA1517, TDA2003 (or TDA 2050) and LM3886. I opt for integrated power amplifiers because, in all fairness, they offer way better quality than anything that can be discretely built (as long as you provide proper cooling and won't let them clip).
Tubes are out of the question for me; however much I like the sound of tubes, they're just a pain in the ass to get right, and the heat and inevitable wear makes them very problematic.
One thing I want to avoid like the plague is ground loops, and thus every connection between independently powered devices (pedalboard, amp head, GT-8, ReAmp input, D.I. outputs) is isolated by using signal transformers, eliminating any chance of forming a hum loop.