Im not positive in case something is wrong with mine, however I didn't receive or have a power cord or port to plug in the power plug. The wiring from the amp to this speaker control should be the power source. Please confirm with Crutchfield.

I have it connected to a "Sonos Connect-amp". This puts out 55w per channel. the SDB-2.1 is then connected to a pair of in-wall Yamaha speakers and a pair of Bose out door speakers. I find that the SDB gives me all the flexibility I want to adjust various volumes. I am totally happy with it. It is made well, the only negative is that the wire connectors are jammed too close together. Not sure the reason for that.

There is no power input required.

The only power it requires is in the incoming signals. There is neither power cord nor battery.

Not that are evident externally for replacement. Also not that I've tripped, using this to attenuate the full load from a power amp, on channels bypassing the pre-amp's volume and tone controls.

I have an Onkyo two channel 85 watt unit in my bedroom for music primarily but also use it for movies. Have a Outlaw Audio sub hooked to the unit and as my main speakers I have a set of older Paradigm 11 towers. The SDB-2.1 is hooked to the receiver via the B speaker output to the input of the SDB-2.1 So I have a Speaker Craft dual pole speaker in the ceiling of my master bathroom, and a set of Paradigm smaller studio monitors on the night stands by the bed, hooked to the SDB-2.1. So I have three sets of speakers hooked to the receiver. So if I want to listen to music I turn on the main unit and have it set for speaker select A/B on and using the SDB/2.1 I can set the volume on the monitors for the best volume balance from front to back speakers listening, The small monitors are about 4 feet from your head, as the 11s are 13 feet from head. And If I want tunes in the bathroom just push a button. Great unit, very good quality, and think I'll buy another unit and set up my guest bedroom the same way. When I built my house a also put a Speaker Craft dual pole speaker in the ceiling of the hall bathroom and the speaker hook-up is the guest bedroom. So I use the SBD-2.1 for the three speaker sound distribution and volume control for my back channel. So when I use the main volume control of the reciever the sound levels stay in synk through the entire volume range of my main unit. Just set the SDB-1 and forget it. Hopes this helps. I'm an analog guy and this thinks rocks. If this doesn't help I can draw a wiring diagram. Let me know.

Ideally you want speakers with matching ohm impedance. The way you have this paired may cause some amplifier performance issues. You will not be able to control the volume independently but you can press the button and turn one pair off or run both pair at the same time but you go back to ohm impedance mismatch. You probably want to call yamaha to make sure you do not damage your amplifier trying to operate it that way.

I fried a tube bass amp many years ago by having the speakers not plugged in. More modern amps may have "no speaker" protection but I wouldn't risk it otherwise. Having said all that, see if the switch loads the second input circuit if nothing is connected - the electronics required ain't rocket science. I have one of those switches which I use with a single solid state amp and 2 speaker zones - fantastic little box.

Don't have the technical knowledge to answer that. But, can say that I have 2 solid state receivers connected and it works great.