I think using the term 'keyboard extension cable' might be confusing, even if it is technically correct. This type of cable hasn't been used for keyboards in 35 years now and two other types of cables have come and gone to serve the purpose of extending keyboard cords in that time (AT and PS/2). If you ask anyone in the computer industry for a keyboard extension cable today, they will most likely hand you a USB extension, and if they are not an idiot, they might just ask you "USB or PS/2?" A DB9 isn't on the list.
So what is it called? It's a serial extension cable(DB9).
On to a tech question... Anyone know if the TIU uses something close to a true RS232 standard port, or does it use TTL level signals like those that a TMCC base provides. Reason for the question is that the TTL level won't like extension cables nearly as much as true RS232 would. Probably fine for 5-10 feet, but much over that and even 9600 baud signals get mucked up with a 5 volt swing.
JGL