Flow could be – channels to groups (with or without compression), groups to main (compressed) or to matrix (bypass compression), main to matrix. This gives you the double-compression flow you’re looking for. If you have groups that you don’t want to compress, you can send them directly to the appropriate matrix and bypass the main output with its compression. Run your speakers or other outputs from the matrix outs, not directly from the main LR.
Another option is to take instrument group outputs and patch back as inputs (presuming you have enough spares), route those to compressed/uncompressed groups, then to mains. As long as you patch back all instrument groups, they will still be phase coherent with each other at the mains.
.
