The IPMux are TDMoIP (Time Division Multiplexer over IP) devices, to transport E1/T1s over an IP network.
The IPMux 8 requires a female DB9 serial cable for it's console, which comes default on 19200 bps. You can see it booting. If your cable doesn't set the DCD, you will see still see it booting, but the IPMux won't accept the data from it. So if you wonder why the IPMuxes don't respond to your keystrokes, make sure you use the cable coming with it!
The IPMux 11 on the other hand requires a male DB9 serial cable, and it set to 115200 bps (note the two differences). If you try to define the timeslots on a bundle on it, and the current bundle is active, it will not accept any changes but will only say "ERROR", while not giving a hint of what the error is. After disabling the bundle, you can edit the timeslots.