You don't happen to have an old ADAT machine laying around, do you?
I purchase a $100 Furman 8 mic pre rack unit. Connect that with 8- 1/4" cables to the ADAT. Set the ADAT to all input monitor and use the ADAT input on the Focusrite Pro40.
I don't have a need for more than 8 mic pres usually, but when I do, it's a cheap means to an end.
The ADAT isn't worth selling, May as well use it for something.
You'll be limited to working 44.1 or 48k due to the ADAT limitation.