HD OMNI recording + routing monitor?

[24BitMusic]

Hi!
HD OMNI
C|24
Focusrite ISA828 + Dig.option

Studioscenario: recording drums, 8 ch going Adat I/O from ISA 828

Now, all channels that OMNI can handle is occupied. How can i get the
vocals, guitar and bassplayer into the monitor section for the drummer?

i have some ideas, but maybe someone tried. I am about to finish the studio
so i am about to hook everything´s up tomorrow....
My idea is to go in thru the C|24 micpre´s, then going line out to a small mixer, then mix the signal from the OMNI with the guitar, vocal etc and send that to the drummers headphone..

OR: i´ll by a used 192 I/O with several I/O´s and the problem solved...