Mine are hidden, but on the back of my transformer cart and not on the layout. But the LEDs and reset buttons are mounted in the fascia of my layout table, remotely from the PSX-ACs.
If you are using a TIU for your MTH Aerotrain you want the PSX-ACs before the TIU (between the Z-1000 and the TIU).
Excellent point. The PSX will not pass the DCS signal. Besides, you want this as close to the power source(s) as possible. Sort of takes care of the "hiding" part.