If I'm interpreting the OP right, he says he wants to use the hardware:
on the way in for my acoustic recordings and as a vocal chain.
(emphasis added).
Sounds like what he has a microphone (or two) and an interface, and he wants to put some 500-series hardware in between, for whatever reason.
My suggestion, for what it's worth:
- One (at least) of the modules should be a mic preamp. A two-channel one, if you want to record with two mics at once (as people often do when recording acoustic guitar). Two one-channel ones would also work, if that's not obvious.
- Plug mic(s) into mic preamp input(s)
- Route signal out of mic preamp through EQ, compressor, etc. in whatever order appeals to you. You generally would do this just by connecting cables to the appropriate jacks on the back of the lunchbox (output -> input, etc.) Some lunchboxes have a switch that allows you to route the signal internally without the cables, so long as you put the modules in the order you want.
- Connect final output(s) to interface input(s) with cable(s)
The lunchbox contains the power supply, and also provides easy connection in the form of standard jacks that you can put cables into. You could use modules without buying a lunchbox if you built your own power supply and wiring; plus you'd probably also want to build some sort of case, so the circuit boards aren't hanging out in the open. Essentially, this is just another way of saying you could use modules without buying a lunchbox if you built your own lunchbox ... which doesn't seem like a particularly promising course of action. As noted, there are other, non-lunchbox-shaped, units you can stick 500-series units in, the most obvious being: (i) a smaller box that allows you to mount a couple modules side-by-side in a standard rack and (ii) a console. The latter will cost considerably more than a lunchbox, and is
probably overkill for your purposes. The former might be useful. Of course, another - perhaps even more useful - approach might be simply to buy standard rack units, rather than 500-series modules. You can even buy a single unit that has mic preamps, an EQ and a compressor already all hooked up in one box.
If you're set on a lunchbox, I will note that some of them sell for quite a bit less than the equivalent of 500 pounds in the US. That, of course, does not mean they do the same thing in Europe, unfortunately.