Harmony 890 RF extender cables

I have the 890 w/ extender and those IR blaster cables,
but can't i use diff cables and plug the extender right into the devices (if compatible) instead of sticking the IR blasters infront of the receivers?

What are these cables called and/or where can i find them?
Or am i completely wrong.
If i am, then Instead of sticking these things to my TV and stereo etc, can i just plug this extender in the room behind me and point one at the TV? or is it only short range? or have to use seperate plugs for each device ( i haven't played with yet cause im trying to find these cables)

(I dont actually need the Extender, i just like not having to point at the TV or worry about being in the room to change the song or someone in the way when i turn on the devices. I just switched from the PS3 bluetooth remote and i miss that feature.)

Thanks in advance for any help/input anyone has

FYI 3.5mm jack doesn't fit between RF extender and PS3 Bluetooth adapter (for whatever reason, they're both Logitch!)
So i had to use the IR blaster tapped over top of it

It worked for my cable box and tv but strangly not for my stereo which was the only one that specifically had a label on the port stating RC input (or something like that.)