Given the IR jack on the 6412 is an output for an IR blaster rather than an IR receiver,
the other solutions I see require external solutions which do not plug into the 6412.
If you search for IR receiver and IR sensor in the forums you'll find some threads
which deal with this.
There were two simple recommendations I liked:
Leapfrog LFIRX remote control extender
Radio Shack wireless remote extender
I'm sure there are other similar products.
These both convert your IR signal to an RF signal in the sender unit, which is
placed outside the cabinet. The RF signal is received by the receiver unit
inside the cabinet, which converts it back to an IR signal. This allows you
to control all the IR units inside the cabinet. These units are intended to
control units which could be as much as 150 feet away. Kind of overkill for
my application but no reason it wouldn't work within a room too.
The other industrial solution for serious home systems involved IR control
boxes which have IR sensors in one room, and drive IR transmitters/blasters
in other rooms. There are numerous threads dealing with these systems,
which are sold on sites like smarthome.