Do you mind telling me the model of the A&H and the focusrite? Do you run individual tracks to the board or busses?
My allen and heath unit is an ice16 It records to a thumbdrive or a hardrive as a stand alone unit, or to a daw. It can be connected via usb or firewire.
As a standalone recording device, you can't do multitrack recording. You can record anything from 1 to16 tracks at once, but no over dubbing. It's great for recording a band off of a board, tape to daw transfers, etc. There are no preamps, which for my uses aren't needed, seeing how I'm using a board.
Side note: firewire gets a lot of shit, but my computer has a great firewire card and I'm real happy with it's performance
The ice16 is run into the line in channels 1 to 16
Currently it's inputs are from the tape machine's outs, although I could hook it up directly to the tape outs of the board.
But the way I'm set up, I record to tape, go out of the tape into the Allen and Heath, out of the A&H into the board.
The other interface is a focusrite pro40. That is fed by the 8 buss outs (but not always)
You asked about effects. Here's my method.
I'll use the first 16 channel's insert points for any effect I want to print to tape. Can also use the insert points on mixdown.
Channels 17 to 20 are used as effects returns, which I usually just use for stereo effects such as reverb or compression that i want to apply to the whole mix.
In practice however, most effects on individual tracks are done in protools.
Let's use compression as an example. With bomb factory (stock protools plugin), that gives me unlimited 1176 style compression,
which in the real world of hardware compressors would be financially impossible.
I'd highly recommend getting some patchbays, if for no other reason than bringing up front all the points on the m520 you want to access.
There's a LOT of jacks back there!