I can only say what worked for me without having to omit any screws and without any other problems with available space, using seven RCA jacks per channel.
I used #4 hardware, that is, #4-40 machine screws and matching #4 hex nuts to mount the I/O PCB to the inside back panel of the PAS.
For the RCA jacks, I used this smaller kind: http://www.parts-express.com/parts-express-gold-rca-jack-solder-type-with-nut-pair--090-278 I believe Velleman also makes RCA jacks this same, smaller size, part numbers CA056R and CA056B.
0.251" (6.375mm) holes in the I/O PCB for mounting the RCA jacks (not the space between holes)
0.125" (3.175mm) holes in the I/O PCB for the #4 screws
If you are using the larger style RCA jacks, then you may have space issues, as you have noted. Or, if you require nine jacks per channel, then, yes, there may be a space issue. Sorry if I could not be of more help.
If I recall, both Roy Mottram and Joe Curcio might offer I/O PCBs with nine jacks per channel? Perhaps you could make inquiries with them.