Hi styxtrekr for your Lightspeed Attenuator to work it's magic it likes to see amps that have an input impedance of >33kohms or more, that would be 99% of amps out there.
Your source should be <1kohm (1000ohms) or less output impedance, again that would be 99% of sources out there.
The interconnect from the Lightspeed Attenuator to the amp should be good quality low capacitance which most are, and 2mts or less in length.
Cheers George