It is annoying, but not uncommon considering that wired IR interfaces lack industry standards (at least standards that are adhered to). This allows manufacturers to set up IR inputs that work only with their own equipment, like Pioneer and Sony, however in this case there's no indication that it shouldn't be directly compatible.

Another annoying aspect of this is that, once you've used the interface block to get the 990 to work, the IR output jack is useless.