Using inputs 11-12 on UA-101?

Hello all, I hope someone can help me figuring this out, because it's driving me insane!
 
I've owned a UA-101 for a few years now and always noticed that on any software you use (nuendo, cakewalk, pro tools, etc) there is always the option to use 12 inputs and 10 outputs but despite trying many, many times, I could never get inputs 11 and 12 to work.
 
Does anybody have any suggestions? I assume that inputs 11 and 12 would connect via the monitor out, normally used for speakers but by disabling this output on the software used for recording. This however doesn't work at all.
 
The owners manual is also very vague and totally unhelpful about this. It mentions inputs 11 and 12 but the only thing it says is "refer to block diagram" which is no good.
 
I couldn't find any info about this on the web hence why I resorted to using the forum in hopes that someone out there figured this one out!
 
Thanks for your help!